Squash, Red Pepper and Corn Gratin with Cheddar Crust

I posted yesterday my solution to some extra cucumbers that were lying around. The orphaned squash situation was worse. So off to my trusty recipe files I went. Eureka! Delicious cheesy squash casserole.

Squash, Red Pepper and Corn Gratin with Cheddar Crust
Makes 8-10 servings.
From Bon Appetit magazine.

Sauce:
2 1/2 tablespoons butter
2 1/2 tablespoons all purpose flour
1 1/2 cups whole milk, hot
3/4 cup (packed) coarsely grated extra-sharp white cheddar cheese
1/4 teaspoon hot pepper sauce

Vegetables:
2 tablespoons olive oil, divided
1 pound medium-size yellow crookneck squash, trimmed, cut into 1/2-inch-thick rounds
1 pound medium-size zucchini, trimmed, cut into 1/2-inch-thick rounds
1 1/4 cups diced onion
1 cup diced red bell pepper
1 garlic clove, minced
1 cup frozen corn kernels, thawed
1 teaspoon chopped fresh rosemary

Topping:
1 1/2 cups (packed) fresh breadcrumbs made from crusty French bread (do not remove crust)
1/2 cup (packed) coarsely grated extra-sharp white cheddar cheese (about 2 ounces)
1 1/2 tablespoons butter, melted

For sauce:Melt butter in heavy medium skillet over medium heat. Add flour and whisk 1 minute. Whisk in hot milk; whisk until mixture boils, thickens, and is smooth, about 5 minutes. Remove from heat. Add cheese and hot pepper sauce and whisk until cheese melts. Season sauce to taste with salt and pepper.

For vegetables:Butter 11x7x2-inch glass baking dish. Heat 1/2 tablespoon oil in large nonstick skillet over medium-high heat. Add half of yellow squash and half of zucchini; sauté until crisp-tender, about 4 minutes. Transfer squash-zucchini mixture to large bowl. Repeat with 1/2 tablespoon oil and remaining yellow squash and zucchini. (Note: If your household prefers softer squash (as my other half definitely does), you might just steam the squash pieces rather than sautéing them.)

Heat remaining 1 tablespoon oil in same skillet over medium-high heat. Add onion, bell pepper, and garlic; sauté until onion is golden and pepper is tender, about 7 minutes. Stir in corn and rosemary. Transfer to bowl with squash-zucchini mixture. Mix in cheese sauce. Season to taste with salt and pepper. Transfer mixture to prepared dish.

For topping:Preheat oven to 400°F. Mix breadcrumbs, cheese, and melted butter in bowl until crumbs are coated with butter. Sprinkle crumbs evenly over gratin. Bake until vegetables are heated through and crumbs are crisp and golden, about 35 minutes.