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My father once asked my mother why she never put cheese in her scalloped potatoes. She told him that the day she did, they would be au gratin, and he could cook them himself. That was the end of it. In our house scalloped potatoes meant thin slices of potato, butter, onion and a creamy milk sauce, baked slowly until the top went golden and the edges bubbled up brown against the dish, and the corner pieces were the ones everybody reached for first.
The trouble most people have with scalloped potatoes is the sauce. It curdles, splits into a thin watery liquid with little white flecks, and the potatoes are either crunchy in the middle or swimming. My mother avoided both with a few rules. She made a proper white sauce with flour, which protects the milk from curdling in the long bake. She warmed the milk first. She sliced the potatoes thin and even and never rinsed them, so their starch thickened the sauce. And she baked the dish covered first, so the potatoes cooked through, then uncovered so the top could brown.
Why this scalloped potatoes works
- A flour-thickened sauce. The flour in a white sauce stabilizes the milk proteins, so the sauce stays smooth through a long bake instead of curdling.
- Warm milk. Adding warm milk to the roux makes a lump-free sauce and avoids the shock that breaks dairy.
- Unrinsed, thin slices. The starch on the potato slices thickens the sauce, and thin even slices cook at the same rate.
- Covered, then uncovered. Steam cooks the potatoes tender first; the open oven at the end makes the golden crust.
- Russet or Yukon Gold potatoes. Starchy potatoes melt into creamy layers. Waxy red potatoes stay firm and separate.
Ingredients
Serves 8 as a side. Baked in a 9x13 inch dish. The measurements are in US cups with grams in brackets.
For the sauce
- 4 tablespoons unsalted butter (56g)
- 1/4 cup all-purpose flour (32g)
- 3 cups whole milk, warmed (720ml)
- 1 1/2 teaspoons fine salt
- 1/2 teaspoon black pepper
- 1 pinch ground nutmeg
For the potatoes
- 3 pounds russet or Yukon Gold potatoes (1.4kg), peeled
- 1 medium yellow onion, sliced very thin
- 2 tablespoons butter, for dotting the top and greasing the dish
Whole milk makes the creamiest sauce. Low fat milk curdles more easily. For an even richer dish, replace one cup of the milk with heavy cream.
How to make scalloped potatoes
Make the sauce
- Heat the oven to 350 degrees (175°C) and butter a 9x13 inch baking dish.
- Warm the milk in a saucepan or in the microwave until steaming but not boiling.
- Melt the 4 tablespoons butter in a saucepan over medium heat, whisk in the flour and cook 1 minute, stirring, without letting it brown.
- Pour in the warm milk a little at a time, whisking constantly, and cook until the sauce is smooth and thick enough to coat a spoon, about 5 minutes. Season with the salt, pepper and nutmeg.
Layer and bake
- Slice the potatoes thin and even, about 1/8 inch thick, by hand or with a mandoline. Do not rinse them.
- Lay a third of the potato slices in the dish, overlapping them, scatter a third of the onion over them, and pour over a third of the sauce. Repeat twice more, finishing with sauce.
- Dot the top with the remaining butter. Cover the dish tightly with foil.
- Bake covered for 50 minutes. Remove the foil and bake 25 to 30 minutes more, until the top is golden, the edges bubble brown and a knife slides through the center with no resistance.
- Let the potatoes rest 10 minutes before serving so the sauce sets around the layers.
Tips that make the difference
- Use the same thickness for every slice. Thick and thin slices together give you crunchy and mushy in the same spoonful.
- Press the layers down gently with a spatula halfway through the uncovered bake so the top slices soak in sauce and brown evenly.
- Put a sheet pan on the rack below to catch drips; a full dish often bubbles over at the edges.
- If the top is pale when the potatoes are tender, slide the dish under the broiler for a minute or two, watching it closely.
Variations
- Au gratin. Stir 1 1/2 cups of shredded sharp cheddar into the sauce and sprinkle more on top. My father would approve, my mother would not.
- Garlic and thyme. Simmer a crushed garlic clove and a few thyme sprigs in the milk, then strain before making the sauce.
- With chicken broth. Replace one cup of the milk with chicken broth for a lighter, savory sauce.
- Smaller batch. Halve everything and bake in an 8 inch square dish, covered 40 minutes and uncovered 20.
Storage and make-ahead
Cover and refrigerate leftovers up to 4 days. Reheat covered in a 325 degree oven with a splash of milk, or in the microwave.
To make ahead, assemble and bake the dish covered, cool and refrigerate overnight, then bake uncovered at 350 degrees for 40 minutes until hot and golden.
Scalloped potatoes do not freeze well; the sauce turns grainy when thawed.
Frequently asked questions
Why did my scalloped potatoes curdle?
Usually the sauce had no flour, the milk was cold or low fat, or the oven was too hot. A flour-thickened sauce made with warm whole milk stays smooth.
What is the difference between scalloped and au gratin potatoes?
Traditional scalloped potatoes are baked in a cream or milk sauce without cheese. Au gratin potatoes have cheese in the sauce and on top.
Why are my potatoes still hard?
The slices were too thick or the dish was not covered long enough. Bake covered until a knife goes through easily, then uncover to brown.
Should I rinse the potato slices?
No. The starch on the slices helps thicken the sauce. Slice them just before layering so they do not turn brown.
Cheese or no cheese is a question every family settles for itself. In ours, my mother settled it once, and the corner pieces still go first.
Old-Fashioned Scalloped Potatoes (Creamy, No Curdling)
Old-fashioned scalloped potatoes with no cheese: thin potato slices layered with onion and a creamy homemade white sauce, baked at 350 degrees covered, then uncovered until golden. A sauce that never curdles.
Ingredients
- 4 tablespoons unsalted butter
- 1/4 cup all-purpose flour
- 3 cups whole milk, warmed
- 1 1/2 teaspoons fine salt
- 1/2 teaspoon black pepper
- 1 pinch ground nutmeg
- 3 pounds russet or Yukon Gold potatoes (1.4kg), peeled
- 1 medium yellow onion, sliced very thin
- 2 tablespoons butter, for dotting the top and greasing the dish
Instructions
- Heat the oven to 350 degrees (175°C) and butter a 9x13 inch baking dish.
- Warm the milk in a saucepan or in the microwave until steaming but not boiling.
- Melt the 4 tablespoons butter in a saucepan over medium heat, whisk in the flour and cook 1 minute, stirring, without letting it brown.
- Pour in the warm milk a little at a time, whisking constantly, and cook until the sauce is smooth and thick enough to coat a spoon, about 5 minutes. Season with the salt, pepper and nutmeg.
- Slice the potatoes thin and even, about 1/8 inch thick, by hand or with a mandoline. Do not rinse them.
- Lay a third of the potato slices in the dish, overlapping them, scatter a third of the onion over them, and pour over a third of the sauce. Repeat twice more, finishing with sauce.
- Dot the top with the remaining butter. Cover the dish tightly with foil.
- Bake covered for 50 minutes. Remove the foil and bake 25 to 30 minutes more, until the top is golden, the edges bubble brown and a knife slides through the center with no resistance.
- Let the potatoes rest 10 minutes before serving so the sauce sets around the layers.
