Potatoes au Gratin | 94.7 QDR

Ingredients

• 1 medium garlic clove, halved
• 3 tablespoons unsalted butter, at room temperature
• 3 pounds medium-size red potatoes, unpeeled and cut into 1/8-inch-thick slices
• 1 medium-size (9 ounce) yellow onion, thinly sliced (about 2 cups)
• 1 tablespoon all-purpose flour
• 1 ¾ cups heavy whipping cream
• 2 ½ teaspoons kosher salt
• 1 teaspoon dry mustard
• ⅛ teaspoon freshly grated nutmeg
• 6 ounces sharp white cheddar cheese, shredded (about 1 1/2 cups), divided
• 4 ounces Gruyère cheese, shredded (about 1 cup), divided
• 2 teaspoons thinly sliced fresh chives