Preheat oven to 190C/Gas 5
1) Mix together all ingredients except 2 tablespoons Cheddar to create a batter in a bowl.
2) In a 25cm cast iron skillet melt butter. Saute onions and broccoli until soft. Pour batter over the vegetable mixture and sprinkle top evenly with remaining cheese. You can also place the ingredients in an 27.5 by 42.5cm baking dish.
3) Bake in oven until golden, 30 minutes.