Potato Gratin

Ingredients

• 5 Garlic Cloves, divided
• 1 tbsp Unsalted Butter, room temperature
• 2 medium Shallots, quartered through root ends
• 2.5 cups Heavy Cream
• 1 tbsp Kosher Salt
• 1 tsp Black Pepper, freshly ground
• 1 tbsp Fresh Thyme leaves, plus more for garnish
• 4 lbs Russet Potatoes, peeled and thinly sliced on a mandolin
• 3oz Gruyere Cheese, finely grated
• 1oz Parmesan Cheese, finely grated