• 1 large Sweet Potato: Peeled and diced into ½ inch cubes. Sweet potatoes bring a natural sweetness, vibrant color, and creamy texture when roasted, forming a delicious and nutritious base for the casserole. They are also packed with Vitamin A and fiber.
• 1 large Head of Broccoli: Cut into florets. Broccoli provides a slightly bitter and earthy counterpoint to the sweetness of the sweet potatoes and adds a wonderful textural element. Broccoli is also rich in vitamins C and K.
• 1 Red Bell Pepper: Cored, seeded, and diced. Red bell pepper adds sweetness, color, and a slight crispness. You can substitute with other colors like yellow or orange for variation. Bell peppers are excellent sources of Vitamin C.
• 1 Yellow Onion: Diced. Yellow onion provides a foundational savory flavor base for the casserole. White or sweet onions can also be used depending on your preference.
• 2 cloves Garlic: Minced. Fresh garlic is crucial for its pungent, aromatic flavor that enhances the overall savory profile of the dish.
• 2 tablespoons Olive Oil: For roasting the vegetables. Olive oil is a healthy fat that helps the vegetables roast beautifully and adds a subtle richness. You can also use avocado oil or another neutral high-heat oil.
• 1 teaspoon Dried Thyme: Thyme adds a warm, earthy, and slightly floral note that complements the vegetables and creamy sauce perfectly. Dried thyme is convenient, but fresh thyme sprigs can also be used (about 1 tablespoon chopped fresh thyme).
• ½ teaspoon Salt: To season the vegetables and enhance their natural flavors. Adjust to taste.
• ¼ teaspoon Black Pepper: Freshly ground black pepper adds a touch of spice and complexity. Adjust to taste.

For the Creamy Sauce:

• 4 tablespoons Butter: Unsalted butter forms the base of the roux for the creamy sauce, providing richness and flavor. For a vegan option, you can use vegan butter or olive oil, though butter provides a classic casserole flavor.
• 4 tablespoons All-Purpose Flour: All-purpose flour is used to create the roux, thickening the sauce and giving it a smooth, creamy texture. For a gluten-free option, you can use a gluten-free all-purpose flour blend or cornstarch (see notes below).
• 3 cups Milk: Whole milk provides the richest and creamiest sauce, but 2% milk or even unsweetened plant-based milk (like oat milk or cashew milk) can be used for a lighter option. Avoid skim milk as it may result in a less creamy sauce.
• 1 cup Vegetable Broth: Vegetable broth adds depth of flavor to the sauce and enhances the overall savory profile. Low-sodium broth is recommended to control the salt content.
• 1 cup Shredded Cheddar Cheese: Sharp cheddar cheese provides a classic cheesy flavor and melts beautifully into the sauce. You can use mild or medium cheddar, or a blend of cheddar and Monterey Jack for a milder, creamier cheese pull. For a vegan option, use a good quality vegan cheddar-style cheese alternative.
• ½ cup Grated Parmesan Cheese: Parmesan cheese adds a salty, nutty, and umami-rich flavor to the sauce. It also contributes to the overall cheesy depth. For a vegetarian option, ensure the parmesan is vegetarian-friendly (rennet-free). For a vegan option, use a vegan parmesan alternative or nutritional yeast for a cheesy flavor.
• ½ teaspoon Garlic Powder: Garlic powder enhances the garlic flavor and adds another layer of savory depth to the creamy sauce.
• ¼ teaspoon Onion Powder: Onion powder complements the garlic powder and adds a subtle oniony note to the sauce.
• Salt and Pepper: To taste. Season the sauce carefully with salt and pepper, as the cheese and broth already contain salt.

For the Crispy Topping:

• 1 ½ cups Panko Breadcrumbs: Panko breadcrumbs are Japanese-style breadcrumbs that are larger and flakier than regular breadcrumbs, resulting in a superior crispy texture. They are essential for that perfect crispy topping.
• ¼ cup Melted Butter: Melted butter is mixed with the panko breadcrumbs to help them brown and crisp up beautifully in the oven. For a vegan option, use melted vegan butter or olive oil.
• ¼ cup Grated Parmesan Cheese: Parmesan cheese adds flavor and helps the topping to crisp up and brown even further. For a vegetarian option, ensure it’s vegetarian-friendly. For a vegan option, use a vegan parmesan alternative or nutritional yeast.
• Optional: ¼ cup Chopped Fresh Parsley: Fresh parsley adds a pop of color and freshness to the topping. It’s optional but recommended for visual appeal and a hint of herbaceousness.

Having all your ingredients prepped and measured before you begin cooking will make the casserole assembly process much smoother and more efficient. Quality ingredients are key to making this vegetarian casserole truly exceptional.