How to Make Béchamel Sauce

Béchamel is a smooth white sauce made by whisking hot milk into a white roux of butter and flour, then simmering until thick. It's one of the five French mother sauces and the base for lasagna, mac and cheese, croque monsieur, moussaka, and gratins.

Why béchamel works

Flour starch thickens milk through starch gelatinization: heated in liquid, the starch granules swell, burst, and release molecules that tangle into a thick, smooth network. The butter coats each flour particle so the starch disperses evenly instead of clumping.

Two details make the difference between silky and pasty:

• Cooking the roux briefly (2–3 minutes) toasts away the raw flour flavour without browning, which would colour and flavour the sauce.
• Simmering after the milk goes in. Starch needs to reach close to the boil to fully thicken, and several minutes at a simmer cooks out graininess and any raw taste.

Milk proteins can scorch on the bottom of the pan, so keep the heat moderate and stir the corners.

Ratios by thickness

Per 500 mL / 2 cups milk:

Lasagna is a judgment call: a medium sauce stays creamy, a thick one sets firmer when sliced.

Steps

1. Warm 500 mL / 2 cups of milk until steaming, in a small pot or in the microwave for about 2 minutes. Don't boil it.
2. Melt 30 g / 2 tbsp of butter in a heavy saucepan over medium-low heat.
3. Whisk in 30 g / 1/4 cup of all-purpose flour and cook for 2–3 minutes, whisking, until it smells like pie crust but hasn't browned.
4. Pour in about a third of the warm milk and whisk hard. It will seize and thicken into a paste, then smooth out.
5. Add the remaining milk gradually, whisking constantly, until smooth.
6. Bring to a gentle simmer, switching to a silicone spatula now and then to scrape the bottom and corners.
7. Simmer 5–10 minutes, stirring often, until it coats the back of a spoon (nappe) and no longer tastes floury.
8. Season with salt (about 1/2 tsp fine salt), a pinch of white pepper, and a small grating of nutmeg.
9. Use right away, or press plastic wrap directly onto the surface to prevent a skin from forming.

For the classic French version, infuse the milk first: warm it with half an onion, a bay leaf, and a whole clove for 10 minutes, then strain before adding it to the roux.

Variations

• Mornay (cheese sauce): Off the heat, stir in 50–100 g grated Gruyère, cheddar, or Parmesan. Add cheese off the heat; boiling makes cheese proteins seize and turn grainy.
• Soubise: Add puréed, slowly cooked onions.
• Nantua: Finish with crayfish butter and cream.
• Cream sauce: Finish with a few tablespoons of heavy cream.
• Mustard sauce: Stir in 1–2 teaspoons of Dijon at the end, great with ham or fish.

Common mistakes and fixes

Lumps. The milk went in too fast or the roux wasn't whisked well. Whisk vigorously; for stubborn lumps, use an immersion blender or press through a fine sieve.

Too thick. Whisk in warm milk a few tablespoons at a time.

Too thin. Simmer longer to reduce. If that doesn't work, knead equal parts soft butter and flour (a beurre manié), whisk in small pieces, and simmer 2 more minutes.

Floury taste. It needs more simmering. Five minutes is a minimum; ten is better.

Scorched bottom. Heat was too high or you didn't scrape the bottom. Pour the sauce into a clean pan without scraping, and taste. If it tastes burnt, start over.

Skin on top. Milk proteins dry out on the surface as it cools. Press plastic wrap or buttered parchment directly onto the sauce, or dot the surface with butter.

Sauce got gluey when reheated. Starch firms as it cools (retrogradation). Reheat gently with a splash of milk, whisking until smooth.

Gluten-free and dairy-free

• Gluten-free: Swap the flour for an equal weight of sweet rice flour, or skip the roux and thicken warm milk with a cornstarch slurry: about 2 tablespoons cornstarch per 500 mL.
• Dairy-free: Use olive oil or vegan butter and unsweetened oat or soy milk. Avoid sweetened or vanilla milks. See the milk substitute guide for more.

Storage

Refrigerate in a sealed container for up to 3 days. Béchamel can be frozen, but the texture may turn slightly grainy; whisk vigorously while reheating to smooth it out.