1. Heat oven to 400 degrees F. Coat a 13 x 9 x 2-inch baking pan with nonstick cooking spray.
2. Trim thin slice from bottoms of tomatoes so they sit level. Slice each tomato horizontally into 4 equal slices. Drain slices on paper towels.
3. Combine in food processor or blender: ricotta cheese, basil leaves, mozzarella, Parmesan, egg yolk, bread crumbs, flour, salt and pepper. Process until smooth.
4. Spread 2 teaspoons cheese mixture on each tomato slice, except the top slice of each tomato. Stack the cheese-covered layers for each tomato, topping each with the plain tomato slice. Insert 2 toothpicks vertically into the top of each tomato to secure the layers together and prevent them from slipping during baking. Transfer to prepared baking pan.
5. Bake in 400 degree F oven for 15 minutes or until the skin just begins to wrinkle on the tops of the tomatoes.Basil Oil:
6. Meanwhile, puree together the olive oil, fresh basil leaves, lemon juice and salt in a small food processor or blender. Let stand for 5 minutes. Strain and discard solids. Drizzle the basil-flavored oil over 6 small salad plates.
7. Let the tomatoes cool slightly. Place 2 tomatoes on each plate. Remove toothpicks and serve. Makes 6 servings.