1/2 cup freshly-grated Parmesan cheese, plus extra for serving
2 cups freshly-grated sharp cheddar cheese*, divided (feel free to add more cheese if you’d like)
4 pounds Yukon Gold Potatoes, sliced into 1/8-inch rounds
2 tsp. fresh thyme leaves, divided
1/2 tsp. black pepper
1 1/2 tsp. Kosher salt
2 cups milk (I recommend 2% or whole milk)
1 cup chicken stock or vegetable stock
1/4 cup all-purpose flour
4 large garlic cloves, minced
1 small white or yellow onion, peeled and thinly sliced
3 tbsp. butter