Move aside mashed potatoes! This creamy potato and onion bake with a mornay sauce is stealing the side dish show this holiday season.
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Potatoes are a staple side dish for any holiday, from mashed to scalloped. This season, I’m introducing a new recipe that blends elements of scalloped potatoes, potatoes au gratin, and dauphinoise potatoes into a unique potato bake.
With a creamy mornay sauce, onions, and a cheesy finish, this dish is decadently delicious and will elevate your holiday menu. Try it yourself and see what all the hype is about!
What Exactly Is a Potato Bake?
This dish is a unique blend of scalloped potatoes, potatoes au gratin, and dauphinoise potatoes.
- Scalloped Potatoes: A simpler version without cheese layers, using a roux of milk, cream, and flour.
- Potatoes Au Gratin: A more decadent dish featuring cheesy layers and breadcrumbs.
- Dauphinoise Potatoes: Made with uncooked, thinly sliced potatoes cooked in a cream sauce.
My potato bake combines uncooked potatoes, layered with onions and a mornay sauce, topped with a mix of cheeses. While it incorporates elements from all three dishes, it stands alone as a delicious potato and onion bake—akin to a casserole but more sophisticated.
What is a Mornay Sauce
You may know about roux and béchamel sauce, but have you heard of mornay sauce?
A roux is a mix of flour and butter, while béchamel sauce is made by adding milk (or heavy cream) and spices like nutmeg to a roux. Mornay sauce is the next step, created by adding grated cheese—typically gruyère and parmesan, though white cheddar can also be used—to béchamel.
How to Make the Mornay Sauce
Start by making the roux: melt six tablespoons of unsalted butter in a large pot over medium heat. Gradually whisk in one-fourth cup of gluten-free all-purpose flour, adding one tablespoon at a time to avoid clumps.
Next, add milk to create the béchamel sauce. I prefer using one 15 oz. can of unsweetened coconut milk. Start by whisking in half the can until smooth, then add the rest.
To transform it into a mornay sauce, mix in three-fourths cup of grated gruyère and half a cup of grated parmesan cheese, adding half at a time and whisking until melted. Fold in the cheese slowly- it will take time to incorporate all of the cheese.
Finally, season the mornay sauce with two teaspoons of 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. Remove from heat once combined.
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 and Onion Bake in a Mornay Sauce
Course: Dinner, SidesDifficulty: Medium11
servings30
minutes2
hoursMove aside mashed potatoes! This potato bake is stealing the side dish show this holiday season.
Ingredients
- For the Mornay Sauce
6 tablespoons unsalted butter
5 tablespoons gluten-free all purpose flour
1 15 oz. can of coconut milk
¾ cup gruyere cheese
½ cup parmesan cheese
2 teaspoons thyme
1 ½ teaspoon black pepper
1 teaspoon salt
¾ teaspoon paprika
½ teaspoon nutmeg
- For the Potatoes
4 russet potatoes, peeled and cut ½" thick
½ white onion, julienned
½ cup gruyere cheese
½ cup parmesan cheese
3 tablespoons unsalted butter, cut into 5 squares
2 teaspoons of freshly minced parsley, for garnish
Directions
- 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 ½" 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
Notes
- Refrigerate in an air tight container for up to four days. To reheat, cook in the air fryer or reheat in the oven.
Callan says
Honestly these potatoes are the best potato I've eaten all year!
I'm typing this as I stand over my oven eating them piping hot out of the casserole dish. Creamy, cheesy, perfectly cooked potatoes. 10/10 would make again.
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