Sauce Champignon (Béchamel, Mushrooms, Crème Fraîche, Lemon)

This 2nd generation mother sauce derives from a finished Sauce Béchamel. Serve with eggs, fish and vegetables.

Sauce Béchamel:
4 Tbsp. butter
4 Tbsp. all-purpose flour, unbleached
2½ cups milk, warmed but not hot
1 pinch nutmeg, freshly grated
¼ tsp. sea salt
⅛ tsp. white pepper, freshly ground

Sauce Champignon:
2 Tbsp. (1 oz) butter (30 g)
1 cup mushrooms, sliced
1 Tbsp. lemon juice, freshly squeezed
¼ cup crème fraîche
sea salt
black pepper, freshly ground

Make the Béchamel Sauce:
Melt the butter in a heavy-bottomed saucepan, add the mushrooms and sauté for a few minutes, until browned. Stir in the flour and cook, whisking constantly, until the paste cooks and bubbles a bit, but don't let it brown - about 2 minutes.

Add the warm milk gradually, continuing to whisk as the sauce thickens. Bring it to a boil. Add nutmeg, salt and pepper. Stir in a blended mixture of crème fraîche and egg yolk. Lower the heat to simmer, and cook, stirring for 2-3 minutes more. Remove from the heat.

Make the Mushroom Sauce:
Heat 1 Tbsp. 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 béchamel.

Remove from heat, swirl in the last 1 Tbsp. of butter.

Makes about 2 cups.