2 cups baking mix (Bisquick)
2/3 cup buttermilk or milk
1 ¼ cups grated Parmesan cheese, divided
2 large tomatoes, seeded and thinly sliced
2 Tbs all-purpose flour
1 small sweet onion, minced and divided
1 cup chopped fresh basil, divided
½ tsp salt, divided
½ tsp pepper, divided
½ cup mayonnaise combined with ¼ cup Dijon mustard
Stir together baking mix and buttermilk in a medium bowl just until blended. Pat into the bottom and up the sides of a lightly greased 9 inch pie plate.
Bake at 400° for 7 minutes. Remove from oven and sprinkle with ¼ cup cheese.
Toss tomato slices with flour, arrange 1 layer of tomato slices over cheese. Sprinkle evenly with half of the onion, basil, salt and pepper. Repeat with the remaining tomato, onion, basil, salt and pepper.
Stir together the remaining 1 cup of cheese and the mayonnaise-mustard mixture, and spread on top of the tomato filling.
Bake at 400° for about 24 minutes or until lightly browned. Let stand 10 minutes before serving.