Preheat your oven to 400°F (200°C).
Bring a large pot of salted water to a boil. Add the Brussels sprouts and cook for 3-4 minutes until just tender. Drain and set aside.
In a baking dish, arrange the Brussels sprouts. Pour the heavy cream over the sprouts.
Sprinkle the grated Gruyère evenly over the top of the sprouts.
In a small bowl, mix the melted butter with the bread crumbs. Sprinkle this mixture over the cheese layer.
Season the gratin with salt, black pepper, and garlic powder.
Bake in the preheated oven for 25-30 minutes, or until the top is golden brown and the sauce is bubbly.
Let cool for a few minutes before serving.