Potato Cheese Casserole

1/2 cup milk
3 eggs, beaten
1/2 teaspoon salt
1/8 teaspoon pepper
1 cup grated cheddar cheese
2 tablespoons butter
1/2 small onion, chopped
3 medium poatoes, grated

Combine all ingredients in a bowl and mix. Pour into casserole dish and bake at 375 degrees for 35 to 40 minutes.