Chop mushrooms fine. In large skillet, melt butter and saute onions until they render their liquid and much of it evaporates. Sprinkle the flour and stir in. Remove from heat and cool 10 minutes. Stir in sour cream and crushed onion soup powder. Turn into a 9" pieplate or quiche dish. Sprinkle with cheddar. This much may be done up to 24 hours ahead. Before serving, bake 25 minutes at 375 degrees. Allow to cool and set up 10 minutes before serving. Serve with toasted pita triangles or melba rounds. Posted to