Potatoes au Gratin | Sides & Appetizer’s | Umami

Ingredients

• 5 garlic cloves, divided
• 1 Tbsp. unsalted butter, room temperature
• 2 medium shallots, quartered through root ends
• 2½ cups heavy cream
• 1 Tbsp. Diamond Crystal or 1¾ tsp. Morton kosher salt
• 1 tsp. freshly ground black pepper
• 1 Tbsp. thyme leaves, plus more for garnish
• 4 lb. russet potatoes, scrubbed, very thinly sliced on a mandoline
• 3 oz. Gruyère, finely grated
• 1 oz. Parmesan, finely grated