Bean and cornbread casserole #2

I'm making a variation on this recipe today.

Serves 4
1 cup polenta
1 cup water (or lime water - see original recipe for details)
1 cup buttermilk or yogurt
3 eggs
1 tsp baking soda
Pinch salt
2 oz grated Parmesan
1 tbsp butter
1 onion, finely chopped
2-3 cups cooked beans (or tinned beans, drained and rinsed)
1 tin chopped tomatoes
3 rashers bacon, chopped (optional)
1 tsp treacle or molasses
1/2 tsp mustard powder
2 oz grated cheddar cheese

Mix the polenta with the water and buttermilk, cover and leave overnight in a warm place. Fry the onions in the butter (or other cooking fat) until soft. Add the bacon and cook. Mix the bacon and onions with tomatoes and stir in the molasses and mustard. You could also add some more veggies to the sauce - sweetcorn and broccoli are going in mine. Place the beans mixture into an ovenproof dish.
Separate the eggs and mix the yolks, baking soda, salt and Parmesan into the polenta. Beat the egg whites until they are stiff and then fold them in. Pour the cornbread batter over the beans. Sprinkle over the cheddar cheese and bake at 375oF for 45-60 minutes (until the bread is set).
Leave out the bacon and use a suitable cheese for vegetarians.