This is an elegant appetizer to serve at cocktail parties, though it isn't difficult to prepare and most of the work can be done ahead of time. They are very delicious! I got this recipe years ago from a co-worker.
Croustades: with a pastry brush, coat the inside of two miniature muffin pans (24 total muffins) with the melted butter.
With a plain or fluted 2 1/2" cutter, cut rounds from the 24 slices of bread; carefully fit them into the muffin tins, pushing the center of the bread into the well and gently molding them around the bottom of the tin Push the tops of the bread rounds into petal shapes; each bread round should form a little cup Bake the croustades at 400° for 10-12 minutes or until they brown slightly on the rims, then remove them from the tins and let them cool.
Duxelles: In a heavy 10-inch skillet, slowly melt the butter; add the shallots, stir them and cook over moderate heat for about 4 minutes.
Add the mushrooms and stir thoroughly to coat them with butter In a few minutes, they will begin to give up a good deal of moisture Stir them from time to time and continue to cook until all the moisture has evaporated, about 10-15 minutes; remove pan from heat; cool slightly.
Sprinkle the flour over the mushrooms and stir until not a trace of flour is visible; pour in the cream.
Put pan back on heat and stir constantly while bringing to a boil; simmer 5 minutes Remove from heat; add salt, parsley, chives and lemon juice.
Use a small spoon or a decorating bag to fill the croustades, mounding the filling slightly; sprinkle each one with a little bit of parmesan cheese.
Before serving, heat the croustades at 350° for about 10 minutes.