1. Combine water, margarine (or butter) and salt in a saucepan. Bring to a boil. Blend flour and cornstarch and add to the water mixture all at once. Using wooden spoon, stir vigorously over Low heat until mixture leaves sides of pan and forms a smooth ball. 2. Remove from heat and add cheese; stir until melted. 3. Add eggs one at a time, beating until smooth and glossy after each one. Transfer to a bowl; cover and chill for 1 hour 4. Grease a baking sheet. Mound the dough in 6 portions on the sheet. Bake in preheated 450-degree oven for 15 minutes, reduce heat to 350 degrees and bake 30 minutes more. 5. Cut a small slit in side of each puff to allow steam to escape. Cool on wire racks. Cut off tops of puffs and fill with your favorite filling, or see "Seafood Sauce" recipe in this cookbook.