Mix flour and salt; cut margarine in until mixture begins to form a ball. Blend in sour cream. Divide dough into 4 parts. Wrap each part and chill several hours.

Heat oven to 350 degrees. On floured board, roll each section into a 12 x 6-inch rectangle. Sprinkle one-half each rectangle with either cheese, onion, mushrooms or olives. Fold dough over to make a 6-inch square. Cut the 6-inch square into 2-inch squares, pressing edges. Continue until all dough is prepared. Bake on ungreased cookie sheet at 350 degrees for 20 to 25 minutes. May be prepared in advance and refrigerated, then baked for 30 minutes. Makes 36 appetizers.