Instructions: Bundle the mushrooms into a clean, dry dishtowel and wring out as much liquid as possible; set aside for the time being.

In a small, heavy saucepan, stir-fry the onion and shallots in the butter over moderately low heat for about 10 minutes, until very soft and golden; do not brown the onion mixture, as this will give the duxelles a tinge of bitterness. Add the mushrooms and suate, stirring now and then, over low heat for about 15 minutes, or until very thick and pastelike. Season with salt and pepper.

Shape the duxelles on a double thickness of foil into a bar about the size of a stick of butter, then wrap snugly and freeze. To use simply slice off 3/4-inch pats (about the equivalent of 1 tablespoon) and use to flavor soups, sauces, gravies, stews, and the like. No need to thaw the duxelles - simply add the frozen pats.

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