1. Sprinkle both sides of tomato slices evenly with salt and pepper. Combine 1 cup buttermilk and egg in a shallow dish, stirring with a whisk. Place flour in a shallow dish. Place cornmeal in a shallow dish.
2. Dredge tomato slices lightly in flour; shake off excess flour. Dip tomato slices in egg mixture; dredge in cornmeal. Heat a large nonstick skillet over medium-high heat 2 minutes. Add 1 tablespoon oil to pan; swirl to coat. Cook 6 tomato slices 2 to 3 minutes or until lightly browned on bottom. Spray tops with cooking spray; turn tomatoes, and cook 3 minutes or until lightly browned. Remove from pan; place on a wire rack. Repeat procedure with remaining oil and tomato slices.
3. Combine 2 tablespoons buttermilk, mayonnaise, and next 3 ingredients (through garlic), stirring with a whisk. Serve with tomatoes.