A variation on Béchamel, this recipe emulates the way the classic sauce was prepared during the 19th century and yields a more nuanced flavor.
2 tablespoons unsalted butter
3 tablespoons finely chopped onion
3 tablespoons finely chopped celery
3 tablespoons finely chopped carrot
2 tablespoons finely chopped prosciutto
1 tablespoon all-purpose flour
1 1/2 cups whole milk
3 flat-leaf parsley sprigs
3 thyme sprigs
1 bay leaf
1/4 teaspoon salt
Dash of freshly ground white pepper
Freshly grated nutmeg (optional)
How to Make It
Place butter in a small saucepan over medium-low heat. Add onion and next 3 ingredients (through prosciutto) to pan, and cook 10 minutes (do not brown), stirring occasionally. Sprinkle flour over onion mixture, and cook 2 minutes, stirring constantly.
Gradually add milk to flour mixture, stirring with a whisk until smooth. Add herbs and bay leaf; bring to a simmer. Simmer 10 minutes or until thickened, stirring frequently. Strain mixture through a fine sieve over a bowl; discard solids. Stir in salt, pepper, and nutmeg, if desired.