5 tablespoons butter
2 tablespoons all-purpose flour
1 cup whole milk
7 ounces common mushrooms, trimmed and sliced
1 tablespoon lemon juice
1 pinch of freshly ground nutmeg
1 pinch fine salt, to taste
1 pinch fresh ground white pepper, to taste
Prepare a sauce béchamel:
Melt 2 tablespoons of butter in a small sauce pan over medium heat. Stir in the flour and cook for a couple of minutes.
Do not allow the flour to brown. Gradually mix in the milk and bring to a low boil. When the sauce is thick and smooth, stir in the nutmeg and pepper. Taste for salt. Keep the sauce at a low simmer until needed.
Prepare the mushrooms:
Heat 2 tablespoons of butter in a fry pan over medium heat.
Add the sliced mushrooms, sprinkle lightly with salt and cook.
Stir often to prevent burning. When the mushrooms start to release water, add the lemon juice and increase the heat to high. When all the liquid has evaporated, add the mushrooms to the sauce. Just before serving, off the heat, stir in the last 1 tablespoon of butter.