This cheesy Broccoli Cauliflower Casserole features both broccoli and cauliflower coated in a creamy cheese sauce that's made healthier by using Greek yogurt. The whole thing comes together in 35 minutes, and is the perfect side dish or meatless meal!
Preheat oven to 400°. Bring a large pot of water to a boil, then add the broccoli and cauliflower and cook for 5 minutes; drain and set aside.
Heat the olive oil in a large skillet over medium heat. Add the leeks and sauté for 3 minutes, then add the garlic and sauté for 2 minutes. Meanwhile, whisk the milk, yogurt, cornstarch, smoked paprika, mustard, salt, and pepper together in a bowl or glass measuring cup.
Pour the milk mixture into the skillet and bring it to a low simmer. Then, sprinkle in the cheese and whisk until smooth; remove from the heat. Pour in the broccoli and cauliflower and stir to combine so that the veggies are coated in the cheese sauce.
Transfer everything to a 9x9 baking dish. Sprinkle the casserole with breadcrumbs and bake it for 20 minutes, then broil for 2-5 minutes until the breadcrumbs are golden brown, being careful not to burn them. Enjoy!