This recipe is sponsored by Birds Eye®. Your guests will ooh and ahh at the rainbow of colors peeking through the blanket of cheese and breadcrumbs in this gorgeous gratin. Purple, orange, green and white cauliflower along with green beans are layered with a cheesy white sauce and then topped with breadcrumbs (and more cheese!). Bake until bubbling for an irresistible upgrade to your typical green bean casserole.
Cook the cauliflower and green beans according to the package directions. Transfer to a colander to drain.
Meanwhile, melt 3 tablespoons of the butter in a large saucepan over medium heat. Add the flour and whisk until bubbling all over, about 1 minute. While whisking continuously, slowly add the milk and continue to cook until the mixture is thick enough to coat the back of a spoon, about 3 minutes more. Whisk in 1 cup of the Cheddar, 1/3 cup of the Parmesan, the nutmeg, 1 teaspoon salt and several grinds of pepper until smooth.
Place half of the cauliflower and green beans in the bottom of a 7-by-11-inch or other 2-quart baking dish, then pour over half of the cheese sauce. Top with the remaining cauliflower and green beans, then the remaining cheese sauce, making sure the vegetables are evenly coated.
Melt the remaining 2 tablespoons of butter in a small microwave-safe bowl, then mix in the breadcrumbs, remaining 1/4 cup shredded Cheddar and remaining 2 tablespoons Parmesan. Sprinkle the breadcrumb mixture over the gratin. Bake until the top is golden brown and the cheese sauce is bubbling at the edges, about 20 minutes. Let cool for 5 minutes before serving.