Homemade Scalloped Potatoes

Bahan-bahan (8 porsi)

• 2 tablespoons unsalted butter
• 1 medium onion (¼-inch diced)
• 6 g arlic cloves (minced (about 2 tablespoons))
• 2 cups whole milk
• 2 teaspoons kosher salt (divided)
• ¼ teaspoon ground black pepper
• 3 pounds Yukon Gold potatoes (about 6 to 8 medium)
• 3 tablespoons all-purpose flour
• 6 ounces sharp cheddar cheese (shredded (about 1 ½ cups))
• 1 ounce Parmesan cheese (shredded (about ¼ cup))