Cauliflower Gratin

Name: Cauliflower Gratin
Ingredients: 2 1/2 cups milk; 1/4 small onion, studded with 1 clove; 1 small bay leaf; 1 small sprig fresh thyme; 5 tablespoons unsalted butter, divided; 3 1/2 tablespoons all-purpose flour; 1 head cauliflower, trimmed and cut into 1 1/2-inch florets (about 7 1/2 cups); 1 teaspoon kosher salt, plus more as needed; 1 generous cup finely grated Gruyere cheese (about 3 ounces); 1 teaspoon Cognac or brandy; Pinch of cayenne; 4 gratings of fresh nutmeg; 1 cup fresh bread crumbs; 1 tablespoon minced fresh flat-leaf parsley