Duxelles
Duxelles is a French cuisine term that refers to a mince of mushrooms, onions, herbs (such as thyme or parsley), and black pepper, sautéed in butter and reduced to a paste. Cream is sometimes used, and some recipes add a dash of madeira or sherry. It is a basic preparation used in stuffings and sauces (notably, beef Wellington) or as a garnish. It can also be filled into a pocket of raw pastry and baked as a savory tart. The flavor depends on the mushrooms used. For example, wild porcini mushrooms have a much stronger flavor than white or brown mushrooms.
Source: Wikipedia