Spicy Cauliflower and Broccoli Gratin

Name: Spicy Cauliflower and Broccoli Gratin
Ingredients: 1/4 cup 1/2 stick butter; 1/4 cup all-purpose flour; 2 cups 2 percent reduced-fat milk; 2 teaspoons spicy brown mustard; 1/4 teaspoon salt; 1/4 teaspoon pepper; 1/4 teaspoon cayenne pepper; 1 1/2 cups shredded jalapeno cheddar cheese; 2 12-oz bags frozen broccoli and cauliflower blend; 1/2 cup chopped green onions