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My mother said there were two potato dishes people always mixed up, and she corrected anybody at her table who called one by the other’s name. Scalloped potatoes have no cheese. Au gratin potatoes do. Scalloped were for plain nights, potatoes and cream and onion. Au gratin were for the nights somebody special came to supper, and the cheese was the reason. She sliced the potatoes thin, layered them in a buttered dish with a cream and cheese sauce, sharp cheddar mostly and a little parmesan on top, and baked them until the sauce bubbled at the edges and the top went deep golden brown. The crisp cheese stuck to the side of the dish was the part my brothers fought over.
The worry with any cheese sauce in a hot oven is that it turns grainy and oily. My mother’s never did. It stayed smooth and creamy down to the bottom layer, because she made a real sauce on the stove first, thickened with a little flour, and took it off the heat before the cheese went in. Flour protects the cheese, and cheese melted off the heat never splits. Here is how to keep the cheese sauce smooth in the oven, and get that crisp golden top.
Why this au gratin potatoes works
- A flour-thickened sauce. A little flour cooked in butter holds the milk and cheese together, so the sauce cannot separate in the oven.
- Cheese melted off the heat. Stirred into the hot sauce away from the burner, the cheese melts smooth instead of turning stringy and oily.
- Block cheese, grated at home. Bagged shredded cheese carries a coating that makes sauces grainy.
- Thin, even slices. Potatoes sliced 1/8 inch thick cook evenly and soak up the sauce.
- Covered, then uncovered. Foil steams the potatoes tender; the last half hour uncovered builds the brown, crisp top.
Ingredients
Makes one 9x13 inch dish, about 8 servings. The measurements are in US cups with grams in brackets.
For the potatoes
- 3 pounds Yukon Gold or russet potatoes (1.4kg), peeled
- 1 tablespoon butter, for the dish
For the cheese sauce
- 4 tablespoons unsalted butter (55g)
- 1 small onion, finely chopped
- 2 cloves garlic, minced
- 1/4 cup all-purpose flour (30g)
- 2 1/2 cups whole milk (600ml), warmed
- 1 cup heavy cream (240ml)
- 1 1/2 teaspoons fine salt
- 1/2 teaspoon black pepper
- 1/4 teaspoon ground nutmeg
- 2 1/2 cups sharp cheddar, grated from a block (250g)
For the top
- 1/2 cup finely grated parmesan (45g)
- 1/2 cup sharp cheddar, grated (50g)
Yukon Gold potatoes hold their slices and give a creamy result; russets are softer and soak up more sauce. Either works. Use a sharp cheddar for the most cheese flavor.
How to make au gratin potatoes
- Heat the oven to 375 degrees (190°C). Butter a 9x13 inch baking dish.
- Slice the potatoes 1/8 inch thick with a sharp knife or a mandoline. Keep them in a bowl of cold water while you make the sauce, then drain and pat them dry.
- Melt the butter in a saucepan over medium heat. Cook the onion for 5 minutes until soft, then add the garlic for 30 seconds.
- Stir in the flour and cook, stirring, for 1 minute.
- Whisk in the warm milk a little at a time, then the cream. Bring to a gentle simmer, whisking, and cook for 3 to 4 minutes until the sauce thickens enough to coat a spoon. Season with the salt, pepper and nutmeg.
- Take the pan off the heat. Stir in the 2 1/2 cups of grated cheddar a handful at a time until smooth.
- Spread a thin layer of sauce in the dish. Lay one third of the potatoes over it in overlapping rows, then pour over one third of the remaining sauce. Repeat twice, ending with sauce, and press the top layer down gently so the sauce covers it.
- Cover the dish tightly with foil and bake for 45 minutes.
- Uncover, scatter the parmesan and remaining cheddar over the top, and bake for 30 to 35 minutes more, until the potatoes are tender when a knife goes in, the sauce bubbles at the edges and the top is deep golden brown.
- Rest for 15 minutes before serving, so the sauce settles and thickens.
Tips that make the difference
- Take the sauce off the heat before adding cheese. Boiling cheese is what makes it oily.
- Dry the potato slices well. Water on the slices thins the sauce.
- Use a dish with low sides for more crisp golden top in every spoonful.
- Do not cut the resting time short. Straight from the oven the sauce is runny.
Variations
- Gruyere. Use half Gruyere and half cheddar for a nutty, more French version.
- Herbs. Add a handful of chopped chives and thyme between the layers.
- Sweet potato. Replace one third of the potatoes with thin sliced sweet potatoes.
- Breadcrumb crust. Mix 1/2 cup breadcrumbs with 2 tablespoons melted butter and scatter over the cheese for the last 20 minutes.
Storage and make-ahead
Keep leftovers covered in the refrigerator for up to 4 days.
Reheat portions in a 350 degree oven, covered, for 20 minutes, then uncovered for 5 to crisp the top.
You can assemble the dish a day ahead, cover and refrigerate it, and add 15 minutes to the covered baking time.
Frequently asked questions
What is the difference between au gratin and scalloped potatoes?
Au gratin potatoes have cheese in the sauce and on top. Scalloped potatoes are baked in cream or a plain white sauce with no cheese. That was my mother’s rule, and most old cookbooks agree.
Why did my cheese sauce turn grainy?
Usually because the cheese boiled or because bagged shredded cheese was used. Thicken the sauce with flour, take it off the heat, and stir in cheese you grated from a block.
How do I know the potatoes are done?
A thin knife slides through the layers with no resistance, the sauce bubbles at the edges, and the top is deep golden.
Can I make au gratin potatoes ahead?
Yes. Assemble, cover and refrigerate up to a day ahead, then bake, adding about 15 minutes to the covered time.
Bake it for the night somebody special comes to supper, and keep the dish with the crisp edges at your end of the table.
Au Gratin Potatoes (Smooth Cheddar Sauce, Crisp Golden Top)
Old-fashioned au gratin potatoes: thin sliced potatoes layered with a smooth homemade cheddar cream sauce and parmesan, baked covered then uncovered at 375 degrees until bubbling and deep golden. The sauce never turns grainy.
Ingredients
- 3 pounds Yukon Gold or russet potatoes (1.4kg), peeled
- 1 tablespoon butter, for the dish
- 4 tablespoons unsalted butter
- 1 small onion, finely chopped
- 2 cloves garlic, minced
- 1/4 cup all-purpose flour
- 2 1/2 cups whole milk (600ml), warmed
- 1 cup heavy cream
- 1 1/2 teaspoons fine salt
- 1/2 teaspoon black pepper
- 1/4 teaspoon ground nutmeg
- 2 1/2 cups sharp cheddar, grated from a block
- 1/2 cup finely grated parmesan
- 1/2 cup sharp cheddar, grated
Instructions
- Heat the oven to 375 degrees (190°C). Butter a 9x13 inch baking dish.
- Slice the potatoes 1/8 inch thick with a sharp knife or a mandoline. Keep them in a bowl of cold water while you make the sauce, then drain and pat them dry.
- Melt the butter in a saucepan over medium heat. Cook the onion for 5 minutes until soft, then add the garlic for 30 seconds.
- Stir in the flour and cook, stirring, for 1 minute.
- Whisk in the warm milk a little at a time, then the cream. Bring to a gentle simmer, whisking, and cook for 3 to 4 minutes until the sauce thickens enough to coat a spoon. Season with the salt, pepper and nutmeg.
- Take the pan off the heat. Stir in the 2 1/2 cups of grated cheddar a handful at a time until smooth.
- Spread a thin layer of sauce in the dish. Lay one third of the potatoes over it in overlapping rows, then pour over one third of the remaining sauce. Repeat twice, ending with sauce, and press the top layer down gently so the sauce covers it.
- Cover the dish tightly with foil and bake for 45 minutes.
- Uncover, scatter the parmesan and remaining cheddar over the top, and bake for 30 to 35 minutes more, until the potatoes are tender when a knife goes in, the sauce bubbles at the edges and the top is deep golden brown.
- Rest for 15 minutes before serving, so the sauce settles and thickens.
