Broccoli Soup au Gratin

Name: Broccoli Soup au Gratin
Prep time: 30 min
Cook time: 35 min
Total time: 1 h 5 min
Cuisine: American
Ingredients: 2 tablespoons unsalted butter, divided; 1 large onion, diced; 3 cloves garlic, minced; 5 cups vegetable broth, or more to taste; 2 pounds broccoli, trimmed; 0.5 cup heavy whipping cream; 2 teaspoons kosher salt, or more to taste; 1 pinch freshly grated nutmeg; 1 pinch ground cayenne pepper, or to taste; freshly ground black pepper to taste; 3 slices country white bread, halved crosswise; 3 cups shredded sharp Cheddar cheese