Scalloped Potatoes

Name: Scalloped Potatoes
Prep time: 15 min
Cook time: 55 min
Total time: 1 h 10 min
Cuisine: American
Ingredients: 3 tablespoons butter; 1 small white or yellow onion (peeled and thinly sliced); 4 large garlic cloves (minced); 1/4 cup all-purpose flour; 1 cup chicken stock or vegetable stock; 2 cups whole milk (or half and half); 1 1/2 teaspoons Kosher salt; 1/2 teaspoon black pepper; 2 teaspoons fresh thyme leaves (divided); 4 pounds Yukon Gold Potatoes (sliced into 1/8-inch rounds); 2 cups freshly-grated sharp cheddar cheese* (divided (feel free to add more cheese if you'd like)); 1/2 cup freshly-grated Parmesan cheese (plus extra for serving)