1 tablespoon unsalted butter
1 tablespoon olive oil
1 small onion, chopped
1 red bell pepper, chopped
2 garlic cloves, minced
2 to 3 yellow squash, chopped
1 medium zucchini, chopped
1/2 cup yellow cornmeal (not self rising)
1/4 cup all-purpose flour
1/4 cup grated Parmesan cheese
1 tablespoon chopped thyme leaves
1 teaspoon kosher salt
1 teaspoon freshly ground pepper
1 cup milk
2 large eggs
2 ounces grated Gruyere cheese
Preheat oven to 350 degrees. Generously butter a casserole or a 9-inch round baking dish. In a large skillet, melt the butter in the oil over moderately high heat. Add the onion and bell pepper and cook, stirring, for 3 minutes. Stir in the garlic and cook until the vegetables are softened but not browned. Add the squash and zucchini and cook, stirring, until almost tender, 4 to 5 minutes. Set aside to cool slightly.
In a large bowl, toss together the cornmeal, flour, Parmesan, thyme, salt and pepper. In a separate bowl, whisk together the milk and eggs, then whisk them into the cornmeal mixture until combined. Stir the vegetables into the loose batter and spread it in the prepared baking dish. Bake on the middle rack of the oven for 30 minutes, or until firm. Sprinkle with the Gruyere and bake for about 8 minutes, or until golden around the edges.