Potato & Onion Bake in a Mornay Sauce
Move aside mashed potatoes! This creamy potato bake with onions and a mornay sauce is stealing the side dish show this holiday season.
An Unbeatable Side for Any Dinner
No matter the holiday, you can always find a side dish of potatoes. From mashed potatoes to scalloped potatoes, this starchy side is always on the menu. And for a good reason! Nothing pairs better with ham for Easter, prime rib for Christmas and turkey for Thanksgiving than potatoes.
This holiday season, we’re mixing things up with a new side dish. This recipe has been a work in progress for a while. At first it was scalloped potatoes, but I found my recipe incorporated aspects of both potatoes au gratin and dauphinoise potatoes. However, it didn’t really fall into any of these three classic potato dishes. Then, I realized it wasn’t any of these recipes- it was it’s own dish! Once I perfected the recipe, I decided to just leave it as simple as possible: a potato bake.
The combination of a creamy mornay sauce, onions, and a cheesy finish make for the perfect side dish. It is so decadent and will make you forget about all other potato dishes! But don’t take my word for it! Make this recipe yourself to find out what all the hype is about.
What Exactly Is a Potato Bake?
This dish is unlike any recipe you’ve had before. While I first started this dish with the intention of making scalloped potatoes, it evolved past the traditional recipe. Scalloped potatoes are often compared to potatoes au gratin or dauphinoise potatoes. There are very small differences that makes these dishes different from one another. And this bake incorporates aspects from each one! So let’s break down exactly what these dishes are and how they vary from each….
- Scalloped Potatoes: This potato recipe is thought of as the “more simple version” of potatoes au gratin. Unlike potatoes au gratin, scalloped potatoes usually do not cheese sprinkled between each layer of the potatoes. Both dishes do use a mixture of milk, cream and flour to make a roux. But au gratin uses cheese and has thinner potato slices.
- Potatoes Au Gratin: This more decadent potato casserole, is known for the cheesy layers. Furthermore, it’s often finished with breadcrumbs and is considered a more decadent dish.
- Dauphinoise Potatoes: The only significant different between this dish and potatoes au gratin is that potato dauphinoise is made with uncooked, thinly sliced potatoes. The potatoes are then cooked in a cream sauce, while potato au gratin is made with pre-cooked thinly sliced potato in a cream sauce.
So, how does this bake differ from these potato dishes? This bake is made of uncooked potatoes, layered with onions and a mornay sauce, then finished with a combination of cheeses on top. While this bake incorporates aspects of all three dishes, it doesn’t fit into the category of any dish. It’s simply and potato and onion bake, much like a casserole but a little more advanced.
What is a Mornay Sauce
You’ve probably heard of a roux and béchamel sauce, but have you heard of a mornay sauce?
If a roux is the first step, and a béchamel sauce is the second, then the mornay sauce is the third. Let’s break this down though. A roux is a combination of flour and butter. A béchamel sauce is traditionally made with milk and a roux. Heavy cream can also be swapped for the milk. A béchamel sauce also features spices like nutmeg. So, the mornay sauce is a béchamel sauce combined with grated cheese. A different combination of cheeses are used to make the mornay sauce. Often times, gruyere and parmesan are used, but sometimes white cheddar is also used.
How to Make the Mornay Sauce
We’ll start by making the roux! Add one six tablespoons of unsalted butter to a large pot or Dutch oven. Melt the butter over medium heat, then reduce the heat once the butter has melted. Slowly whisk in one fourth cup of gluten-free all purpose flour, one tablespoon at a time. It’s important to go slow. If you add all the flour at once, the roux can break or become clumpy. Once all the flour is incorporated, we have our roux!
Next up, adding the milk to make the béchamel sauce. While you can use milk or heavy cream, I like to use coconut milk instead. It’s a lot less heavier than cream but a great substitution! Add one 15 oz. can of unsweetened coconut milk to the roux. Add half the can of coconut milk, and whisk. It may look like the sauce has curdled but it hasn’t. Just keep whisking until it becomes smooth. Then, add the rest of the coconut milk and whisk again to combine.
Finally, we’re going to take our sauce from a béchamel to a mornay sauce. To make the mornay sauce, we will be using three fourths cup of freshly grated gruyere cheese and one half cup of grated parmesan cheese. Add half of the cheese to the sauce and whisk. Fold in the cheese slowly- it will take time to incorporate all of the cheese. Once the cheese has melted and combined with the sauce, add the rest of the cheese. Whisk again to fold in the cheese.
The last step is adding in the spices to the mornay sauce. Season with two teaspoons dried thyme, one and a half teaspoons of black pepper, half a teaspoon of nutmeg, three fourths teaspoon of paprika, and one teaspoon of salt. Once the seasonings are mixed in, remove the sauce from the heat.
Layering the Potatoes
Before we can layer the potatoes, we first need to prepare the baking dish. Take a nine by thirteen inch baking dish and grease it. Make sure you grease the edges too as the potatoes will be stacked to the very top! Then, preheat the oven to 375 degrees Fahrenheit.
Now, it’s time for the potatoes! Start by washing and peeling four russet potatoes. Then use a mandolin slicer to cut the potatoes into half an inch thick slices. This not only ensures that each potato is the same thickness, but also makes the process much quicker! Once all of the potatoes are sliced, set them to the side. Julienne half of a white onion and place by the potatoes.
To layer the potatoes, start by covering the bottom of the dish with about 3-4 rows of potatoe, laid against one another to create a domino effect. Once there’s a layer of potatoes, sprinkle the julienne white onion over the potatoes. There should be roughly five to ten pieces of onion spread out over the potatoes. Finally, whisk the mornay sauce and pour it over the potatoes and onions. Pour a little less than one fourth of the sauce over the layer, then use a spatula to disperse it. Repeat this process until you get to the very top of the dish and have done your final layer of potatoes, onions, and mornay sauce. To finish the dish, sprinkle a mixture of half a cup of grated parmesan cheese and half a cup of grated gruyere cheese over to the top.
The Last Steps
Before you pop the potato and onion bake in the oven, slice three tablespoons of butter into five even pieces. Place four pieces of the butter on the edges of the dish and one in the center. This will prevent the edges from burning and ensure the center of the dish is perfectly crispy. Cover the bake with foil and place it in the center of the oven. We’re going to bake the potatoes for an hour and a half covered at 375 degrees. After the allotted time, remove the foil and allow the potatoes to cook for another 15 minutes uncovered. Finally, broil the potatoes on high for five minutes . Once the potatoes are golden brown, turn off the oven and remove the dish. Make sure to watch the potatoes closely as they can burn quickly on broil!
Allow the dish to cool for at least twenty minutes. Finally, before you serve the potato and onion bake, garnish with freshly minced parsley.
Potato & Onion Bake in a Mornay Sauce
For the Mornay Sauce
- 6 tablespoons unsalted butter
- 5 tablespoons gluten-free all purpose flour
- 1 15 oz. can of coconut milk
- 3/4 cup gruyere cheese
- 1/2 cup parmesan cheese
- 2 teaspoons thyme
- 1 1/2 teaspoon black pepper
- 1 teaspoon salt
- 3/4 teaspoon paprika
- 1/2 teaspoon nutmeg
For the Potatoes
- 4 russet potatoes, peeled and cut 1/2″ thick
- 1/2 white onion, julienned
- 1/2 cup gruyere cheese
- 1/2 cup parmesan cheese
- 3 tablespoons unsalted butter, cut into 5 squares
- 2 teaspoons of freshly minced parsley, for garnish
- For the Mornay Sauce
- Heat your butter in a large pot over medium heat
- Once melted, reduce the heat to low and slowly whisk in the flour – one tablespoon at a time
- After the flour is incorporated, the roux should be thick. Pour in half the coconut milk and whisk to combine. Once combined, add the rest of the coconut milk
- Fold in half the cheese and stir until incorporated into the béchamel sauce
- Then, fold in the rest of the cheese
- Whisk in the spices, then remove from heat
- For the Potatoes
- Preheat your oven to 375 degrees Fahrenheit and spray a 9″ by 13″ baking dish with nonstick spray
- Wash and peel the potatoes, then use a mandolin to slice the potatoes into 1/2″ thick pieces
- Next, julienne your white onion and set to the side
- Begin layering the potatoes on the bottom of the dish, laying against one another and making three to four rows along the dish
- After the first layer of potatoes is down, add 5-10 pieces of the julienned onion
- Then pour a little less than one fourth of the mornay sauce over the potatoes and onions. Use a spatula to spread the sauce over the vegetables.
- Repeat for the next three layers
- Once the final layer is finished, sprinkle the gruyere and parmesan cheeses over the top
- Place the butter squares along the four edges of the baking dish and place one square in the middle
- Cover with aluminum foil, and bake for 75 minutes
- Remove the foil, and bake for another 15 minutes until the cheese is bubbling
- Finally, broil on high for 5 minutes until golden brown
- Allow to cool for 20 minutes then finish with freshly minced parsley
- Refrigerate in an air tight container for up to four days. To reheat, cook in the air fryer or reheat in the oven.