Preheat the oven to 425 degrees F.
In a 12 to 14-inch saute pan, heat the olive oil over high heat and add the onion and salt and pepper, to taste. Cook until the onion is softened and golden brown, about 5 minutes. Add the tomatoes and cook until the tomatoes break down and exude their juices, about 10 minutes. Remove from the heat.
In a large bowl, combine the corn flour, corn kernels, ricotta, skim milk, baking powder, and tomato sauce and stir well. Grease a casserole with the butter and turn the mixture into the casserole. Bake for 1 hour.
Recipe copyright 2001, Mario Batali. All Rights Reserved.