Preheat oven to 400F. Grease and lightly flour large baking sheet. Combine water, 1/2 cup margarine and salt in saucepan. Bring to boil over medium heat. Add flour all at once. Stir vigorously with wooden spoon until smooth and dough forms a ball and leaves side of pan. Remove from heat.
Add eggs, 1 at a time, stirring until smooth after each addition. Spoon dough into large pastry bag fitted with fluted nozzle. Pipe dollops of dough, about 1 tablespoon each, onto prepared baking sheet, leaving room for spreading. Bake 20-25 minutes until golden brown. Let cool.
Melt 2 tablespoons butter/margarine in a large skillet. Add onions and mushrooms; saute over medium-low heat until tender. Stir sour cream into onion mixture; let cool.
Cut baked pastry swirls in 1/2 horizontally. Using a spoon or small paring knife, remove any soft dough inside puffs, leaving a hollow, 2 part shell or crust about 1/4 to 3/8 inch thick. Spoon about 1 tablespoon sour cream mixture in bottom portion of each swirl. Replace top portion of swirls.
Preheat oven to 350F. Bake on large baking sheet 10 minutes or until heated through.