Preheat your oven to 180°C (350°F). Lightly butter or spray your 9x13 inch baking dish to prevent sticking.
Trim the broccoli into bite-sized florets, then toss them with a drizzle of olive oil, salt, and pepper. Spread on a baking sheet and roast for 15–20 minutes until slightly charred and fragrant. This deepens the broccoli’s flavor and helps it stay tender yet firm in the casserole.
While the broccoli roasts, grate the sharp cheddar cheese until you have about 1 ½ cups. Set aside for layering and topping.
In a large mixing bowl, whisk together the cream of mushroom soup, sour cream, onion powder, and lemon juice until smooth and well combined. This creates a creamy, tangy base for the casserole.
Once the broccoli is roasted and cooled slightly, add it to the bowl with the soup mixture. Gently fold to coat all the florets evenly, then sprinkle in most of the grated cheese, folding again to incorporate.
Transfer the mixture into your prepared baking dish and spread it out evenly with a spatula. Sprinkle the remaining cheese over the top for melty goodness.
In a small skillet, melt the butter over medium heat, then add the breadcrumbs. Toast, stirring constantly, until golden brown and crispy, about 3–4 minutes. Sprinkle the toasted breadcrumbs evenly over the casserole for a crunchy topping.
Bake the casserole uncovered in the preheated oven for 25–30 minutes, until bubbling and golden on top. Cover loosely with foil if it starts to brown too quickly.
Once baked, remove the casserole from the oven and let it rest for 10 minutes. This helps it set and makes slicing easier. The top will be golden and crispy, with tender broccoli peeking through the cheesy sauce.
Garnish with additional cheese or herbs if desired, then serve warm. Enjoy the perfect balance of crispy topping, creamy interior, and roasted broccoli flavor.
