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.
Remove from heat and add cheese; stir until melted.
Add eggs one at a time, beating until smooth and glossy after each one. Transfer to a bowl; cover and chill for 1 hour.
Grease a baking sheet. Mound the dough in 6 portions on the sheet. Bake in preheated 450° F oven for 15 minutes, reduce heat to 350° F and bake 30 minutes more.
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.Servings: