Brush off the debris from a pound of mushrooms and slice them thinly. Thinly slice a half-pound of shallots. Saute the shallots first, then add the mushrooms, in 2-4 tablespoons of olive oil, butter or a mixture of the two. Do not use light butter or margarine; they have too much liquid whipped into them and won't freeze as well. Cook over low heat until almost a paste, seasoning with salt, pepper, chopped parsley and thyme as desired. For extra flavor, add a cup of white wine or chicken broth and continue cooking until all the liquid has evaporated. Cool, pack in small containers or the above-mentioned ice cube trays, and freeze.
Why did I think of this today? Maybe it's the foodie in me, but when I see Dulles, I think duxelles, pronounced dook-SEHL, the French name for this dish.