Preheat the oven to 400 degrees F and butter a 2-quart baking dish.

Bring a large pot of salted water to a boil.

Add the Brussels sprouts to the boiling water and cook until tender, about 8-10 minutes.

Drain the Brussels sprouts thoroughly.

Coarsely chop the drained Brussels sprouts.

Transfer the chopped Brussels sprouts to the prepared baking dish.

Toss the Brussels sprouts with red pepper flakes, salt, and pepper to taste.

Spread the seasoned Brussels sprouts evenly in the baking dish.

Pour heavy cream over the Brussels sprouts.

Sprinkle grated white cheddar cheese evenly over the cream.

Sprinkle breadcrumbs evenly over the cheese.

Dot the top with pieces of unsalted butter.

Bake the gratin in the preheated oven until bubbly and golden brown, about 15 minutes.

Let cool slightly before serving.