- 1/2 stick unsalted butter
- 1/4 cup flour
- 2 cups milk
- 1/4 cup Parmesan cheese, grated
- 1/4 cup Swiss cheese, grated
- 2 egg yolks
- 1/2 stick butter
- kosher salt and black or white pepper to taste
- Melt butter in a small saucepan. Slowly blend in flour.
- Gradually stir in the milk and cook, stirring constantly over medium heat until the mixture comes to a boil and thickens.
- Reduce heat, add Parmesan and Swiss cheese and stir until the cheese melts. Remove from the heat.
- When ready to serve, beat the egg yolks lightly in a small bowl. Gradually add small amounts of the hot milk mixture to the egg, stirring constantly, until until the bowl feels warm to the touch.
- Then slowly stir egg mixture into the milk mixture.
- Cut the butter into small pieces and stir into the sauce. Season with salt and pepper.
- Do not reheat the sauce after adding the egg yolks or it will curdle.
- Makes 2 and 1/2 cups.