How to Make Classic Béchamel
In a heavy-bottomed saucepan, melt the butter over low heat.
Add the minced onion and cook gently, stirring often, until soft and translucent but not browned.
Stir in the flour to create a paste, known as a roux.
Continue cooking for 2-3 minutes, stirring constantly. This step is crucial to cook out the raw flour taste.
Gradually pour in the hot milk while whisking vigorously to prevent lumps.
Continue whisking until the sauce is completely smooth and begins to thicken.
Add the peppercorns, thyme, bay leaf, a pinch of salt, and a dash of nutmeg.
Reduce the heat to the lowest possible setting and let the sauce gently simmer for at least 15 minutes, or up to an hour for a richer flavor.
Stir occasionally to prevent it from sticking.
Strain the sauce through a fine-mesh sieve to remove the onion and herbs for a silky-smooth finish. To prevent a skin from forming, dot the surface with small pieces of butter. Your Béchamel is now ready to use!
How to Make a Richer Béchamel
In a separate bowl, whisk together the heavy cream and egg yolks.
While whisking continuously, slowly temper the mixture by gradually pouring in about 1 cup (240 ml) of the hot, prepared Béchamel sauce.
Pour the tempered egg mixture back into the main saucepan with the rest of the Béchamel, whisking constantly.
Heat the sauce over very low heat, stirring and scraping the bottom of the pan, until it thickens and just comes to a simmer.
Do not let it boil, or the eggs may curdle.
Remove from the heat.
Stir in the lemon juice and season with additional salt if needed. For an extra decadent finish, whisk in the optional 2 tablespoons (30 ml / 1 fl oz) of butter, piece by piece, just before serving. Note: Do not use the butter enrichment if you plan to bake the sauce in a gratin, as it may separate.
Don't skip cooking the roux for a few minutes after adding the flour. This simple step toasts the flour and gets rid of any raw, pasty taste.