_Salsa Bianca_
1 tablespoon flour or cornstarch
1/4 cup butter
1 tablespoon vinegar
Salt and pepper
1/2 cup water or soup stock
Yolk of 1 egg
Melt half the butter, add the flour and cook until it begins to brown.
Add the water slowly, stirring meanwhile, the vinegar and the rest of
the butter. Take from the fire and add the beaten egg yolk. This sauce
should be smooth like a thin custard.