In a 3-quart saucepan, cook onion in butter till tender but not brown. Stir in flour. Add water. Cook and stir till thick and bubbly. Blend in cheese spread. Remove from heat. Stir in broccoli, then eggs. Transfer to a 1-1/2-quart casserole. Top with cornflakes.
Bake, uncovered, in a 325 degree oven for about 50 minutes or until knife inserted halfway between edge and center comes out clean. Let stand 10 minutes before serving. Makes 8 servings.