Mix flour and 1/4 cup brown sugar in a large ziploc or other clean plastic bag. Insert breasts and shake until coated with mixture.
Heat butter and olive oil in a large skillet over medium-high heat. Place chicken in skillet and cook, turning once to brown both sides. Sprinkle remaining brown sugar on the chicken while cooking.
Stir in onions and garlic, cook until onions are clear and soft--usually about 4 minutes. Stir in tomatoes and wine; bring to a boil. Then stir in curry, white sugar, and salt/pepper to taste. Cover, and cook over medium-low heat for 15 minutes or so.