Slice tomatoes about 1/2 inch thick. Brush with mayonnaise; sprinkle with salt and pepper. Combine 1/3 cup each cornmeal and all-purpose flour, and 2 tbsp. grated Parmesan cheese; dredge tomatoes in mixture. Drop 2 tbsp. butter on rimmed baking sheet; place in a 450 degree oven until butter is melted. Place tomatoes on pan; bake for 8 minutes per side or until golden.