Potato and Celeriac Gratin Dauphinois

Ingredients

• 2 cups whole milk
• 1 cup heavy cream
• 4 oz . freshly grated Swiss Gruyere cheese
• Sea salt and freshly ground pepper to taste
• Freshly grated nutmeg to taste
• 1 large garlic clove (, peeled and halved)
• 2 lbs . firm fleshed potatoes (, peeled and sliced very thin)
• 1 celeriac (, peeled and sliced thinly)
• 3 tbsp butter