Use a small cookie cutter to cut rounds out of the bread. Press the rounds into ungreased mini muffin tins, and bake for 8 or 9 minutes until golden; keep a close watch on them, as they bake fast. Turn out bread cups to cool.
Heat butter in a large skillet over medium heat. Stir in the mushrooms and onions, and cook until soft, about 8 minutes. Season with cayenne pepper, lemon juice, salt, pepper, and chopped parsley. Gradually stir in half-and-half, and sprinkle with a bit of flour until mixture gets thick.
Fill bread cups with mushroom mixture, top each with a sprinkle of Parmesan, and place on a lightly greased baking sheet. Bake for 10 to 12 minutes.
