Sauté onion in butter; stir in mushrooms and cook until liquid evaporates. Add lemon juice, salt and pepper. Combine cornstarch and water; add to mushroom mixture. Add cream and stir until thickened.

Unroll crescent dough, shape into a rectangle and cut into 24 squares; carefully press each square into greased mini muffin cups. Fill with 1 tablespoon of mushroom mixtures. Sprinkle with Swiss cheese. Bake at 350degrees for 15 minutes or until browned on edges and filling is set. Remove from pan and serve on platter.