Crockpot Scalloped Potatoes

Bahan-bahan (8 porsi)

• 2 ¾ cups Yukon Gold potatoes (peeled, 1/4-inch-sliced (about 1 pound or 3-4 medium potatoes)*)
• 2 ¾ cups sweet potatoes
• Kosher salt (about 1 1/2 to 2 teaspoons, plus 1/4 to 1/2 teaspoon for the sauce)
• Freshly ground black pepper (about 1 to 1 1/2 teaspoons for the potatoes, plus 1/8 to 1/4 teaspoon for the sauce)
• 4 tablespoons unsalted butter ((1/4 cup))
• ¼ cup finely diced yellow onion (about 1/2 of a small onion)
• ¼ cup all-purpose flour
• 2 cloves garlic (minced (about 1 teaspoon))
• 2 cups nonfat milk
• ¼ teaspoon freshly grated nutmeg**
• 1 cup freshly grated sharp cheddar cheese*** ((about 2 1/2 ounces))
• 2 teaspoons chopped fresh thyme
• ¼ cup freshly grated Parmesan cheese