Preheat the oven to 425°F (220°C). Line a rimmed baking sheet with parchment for easy cleanup.
Cut the broccoli into florets keeping ~1-inch stems for texture. Toss the florets with 2 tablespoons olive oil, 1 teaspoon salt, and ½ teaspoon black pepper in a mixing bowl until evenly coated. Spread the broccoli in a single layer on the sheet.
Roast the broccoli for 10–12 minutes, shaking the pan halfway so the edges brown evenly. You want tender stalks with crisp, caramelized tips.
Mix the topping: In a small bowl, stir together melted butter, panko, Parmesan, and crushed red pepper flakes. Set aside.
Transfer roasted broccoli to a baking dish (or leave on the sheet if oven-proof). Sprinkle shredded sharp Cheddar across the broccoli so it melts over the florets. Scatter the panko-Parmesan mixture evenly on top.
Broil briefly: Place the casserole under the broiler for 2–3 minutes until the cheese bubbles and the crumbs turn golden. Watch carefully — it goes from golden to burnt fast.
Serve immediately with an extra crack of black pepper and, if you like, a quick squeeze of lemon to cut the richness.
Pro tip: If you want extra toasty panko, toast it in a dry skillet for 2 minutes before mixing with butter
