Cauliflower and Bacon Gratin

Name: Cauliflower and Bacon Gratin
Ingredients: Unsalted butter, for dish, plus 1/2 stick (4 tablespoons), cut into 1/2-inch pieces; 3 slices day-old sourdough bread or 2 cups bread crumbs; 3/4 cup heavy cream; 1 teaspoon all-purpose flour; 1/4 cup capers, rinsed and drained; 8 ounces bacon, cooked until crispy and cut into 1/2-inch pieces; 1 cup grated Gruyere, divided; Kosher salt and freshly ground black pepper; 1 pound cauliflower, trimmed and cut into florets; Olive oil, for drizzling