Preheat oven to 350F.
Grease a 2 quart casserole.
Saute the onion in butter until soft but not brown.
Add the bread cubes and brown sugar,
stirring over low heat for 3-5 minutes.
Stir in the tomatoes;
season with salt and pepper to taste.
Put the tomatoes in the prepared casserole
and bake at 35F for 30 to 40 minutes
or until the casserole is bubbly.