Instructions:

Preheat oven to 400°. In a large saucepan, cook macaroni according to package directions. Immediately rinse with cold water to stop the cooking process. Drain and set aside. Meanwhile, in a medium non-stick skillet, melt 2 tablespoons butter over high heat. Add the onion, celery, and bell pepper and cook until vegetables are soft and transparent. Remove from heat and set aside.

In a large mixing bowl, stir together the cornbread mix, milk, 2 tablespoons melted butter, and eggs until combined. Stir in 1 cup of the shredded cheese and the vegetable mixture. Spray a 13 x 9-inch glass baking dish with nonstick cooking spray. Pour cornbread mixture into the casserole dish. Set aside.

In a large heavy saucepan, melt 1/4 cup butter over medium to high heat; add flour and whisk for 1 minute. Gradually whisk in milk; continue to cook over medium to high heat stirring constantly, until thickened and bubbly. Stir in the salt, pepper, and 3 cups of the shredded cheese, until melted. Stir in the macaroni. Carefully spoon macaroni mixture over cornbread, gently pressing macaroni into cornbread batter with the back of a large spoon. Sprinkle with remaining 1 cup shredded cheddar cheese. Stir together the crushed pretzels and 1/4 cup melted butter. Sprinkle on top of cheese. Bake for 30 minutes or until golden brown on top and bubbly around edges.