Delicious Au Gratin Potatoes Recipe - The Trellis

Ingredients

• Russet potatoes, thinly sliced (1/8-1/4 inch thickness)
• 6 tablespoons unsalted butter
• 1 small onion, finely chopped
• 2 cloves garlic, minced
• 3 tablespoons all-purpose flour
• 2 cups chicken stock
• 2 cups whole milk
• 1 teaspoon black pepper
• 1 teaspoon salt
• Fresh thyme, divided
• 2 cups shredded cheddar cheese
• 1/2 cup grated Parmesan cheese