Duxelles is a French mushroom dish.
For basic duxelles, mince 1/2 pound fresh mushrooms (or mushroom stems) and 1 small onion or 1 to 2 shallots. In a frying pan, sauté the onion or shallot in 1 to 2 tablespoons butter until soft but not brown (3 to 5 minutes). Stir in minced mushrooms, salt and pepper, chopped parsley to taste, and a pinch of tarragon or thyme if you wish. Depending on your main course, any fresh herb(s) or splash of soy sauce, white wine, Madeira, lemon juice, or even fruit, such as dried apricots, can be added. Cook the mixture over medium high heat until the mushrooms give off a lot of liquid; that liquid will evaporate completely (5 to 10 minutes). The duxelles will look like a coarse mash. Cool the mixture slightly and taste for seasoning. This will make about 1-1/2 cups. Duxelles may be frozen for 1 to 2 months.
If you're using dried mushrooms, rinse them first as they are almost always holding grit and bits of the forest from which they grew; then soak them in very hot (but not boiling) water (add heated wine or fruit/vegetable juice if you want more flavor) until tender (10 to 20 minutes, depending on how large they are). Remove them from the water; rinse and again scrub them well with a mushroom brush. Pat the mushrooms dry and continue as for fresh mushrooms.
Sauce duxelles is made starting off with a basic duxelles recipe, and then adding white wine, stock and tomato purée. This is served over fish, meat or eggs.