Ravioli with Butter, Walnuts, and Sage

The secret to this sauce, which is popular in Tuscany, is to cook the butter until it browns but not until it burns, which gives the sauce a nutty flavor. You can use any kind of nuts you like—pine nuts are wonderful but cost a fortune, and pistachios look great—and you can substitute different herbs, such as chopped marjoram or thyme, for the sage. This ravioli filling is traditionally flavored with nutmeg, but you can instead flavor it with an herb, such as chives, chervil, or thyme.