Creating the Vegetarian Broccoli and Cheddar Pasta Casserole is simple when you follow these steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C).
2. Cook the Pasta: In a large pot of salted boiling water, cook the pasta according to package instructions until al dente. Drain and set aside.
3. Blanch the Broccoli: In the same pot, blanch the broccoli florets in boiling water for 2-3 minutes until bright green. Drain and set aside.
4. Sauté the Vegetables: In a large skillet, heat olive oil over medium heat. Add chopped onion and sauté until translucent, about 5 minutes. Stir in minced garlic and cook for an additional minute.
5. Make the Cheese Sauce: In a mixing bowl, combine 1 cup of shredded cheddar cheese, milk, vegetable broth, Dijon mustard, salt, black pepper, and paprika. Whisk until smooth.
6. Combine Ingredients: In a large mixing bowl, combine the cooked pasta, blanched broccoli, sautéed onions and garlic, and the cheese sauce. Stir until well combined.
7. Transfer to Baking Dish: Pour the mixture into a greased 9×13-inch baking dish. Spread evenly.
8. Add Topping: If desired, sprinkle breadcrumbs and remaining shredded cheddar cheese over the top for a crispy finish.
9. Bake: Place the casserole in the preheated oven and bake for 25-30 minutes, or until bubbly and golden brown on top.
10. Cool and Serve: Remove from the oven and let it cool for a few minutes before serving.

By following these steps, you will create an incredible Vegetarian Broccoli and Cheddar Pasta Casserole that everyone will love!