My mother made this regularly for Sunday lunch!
1 medium egg
1 dash each salt, pepper, and Cayenne pepper
1 cup aged Cheddar cheese, grated
1/3 cup milk
1 medium onion, chopped
In a mixing bowl, beat together milk and egg. Pour into a saucepan and bring to a boil. Once boiling, add the rest of the ingredients and stir until thick. Pour on hot toast and enjoy!