Potatoes Au Gratin - Jo Cooks

Ingredients

• ¼ cup butter (unsalted)
• 1 medium onion (chopped)
• 3 cloves garlic (minced)
• ¼ cup all-purpose flour
• 1 cup chicken broth (low sodium or no sodium added)
• 2 cups whole milk (or half and half)
• ½ teaspoon salt (or to taste)
• ½ teaspoon pepper (or to taste)
• 1 tablespoon fresh thyme (chopped, for garnish)
• 3 pounds potatoes (sliced into ⅛-inch rounds, I prefer Yukon Gold)
• 2 cups white cheddar cheese (freshly grated)
• ½ cup Parmesan cheese (freshly grated)