Creamy Potato Gratin with Cheese

Ingredients

• 3 tablespoons butter
• 1 small onion, finely diced
• 1 clove garlic, minced or grated
• 1 teaspoon fresh thyme, chopped or 1/2 teaspoon dried thyme
• 3 tablespoons flour (use gluten-free flour for a gluten-free option)
• 1 1/2 cups milk or heavy cream
• 1 1/2 cups Gruyere cheese, shredded
• 1 pinch nutmeg, optional
• salt
• pepper
• 4 pounds potatoes, thinly sliced