1-Preheat the oven to 375ºF (190°C) and lightly brush a 10-inch cast-iron skillet with 1 tablespoon olive oil to prevent sticking.

2-Peel and very thinly slice 3 medium sweet potatoes and 6 small Yukon gold potatoes using a mandolin or vegetable slicer for even results.

3-Gently toss the potato slices in a large bowl with 1 teaspoon kosher salt, 1/4 teaspoon ground black pepper, 3/4 teaspoon garlic powder, 1/2 teaspoon dried thyme, 1/2 teaspoon ground sage, 1 1/2 teaspoons dried parsley (or 1-2 tablespoons fresh), 1/2 teaspoon dried rosemary (or 2 teaspoons fresh), most of the 8 ounces grated Gruyère or sharp white cheddar cheese (reserve some for topping), and 1/2 cup chopped yellow onion, being careful not to break the slices.

4-Arrange small handfuls of the coated potatoes sideways in the skillet, layering them evenly for a uniform bake.

5-Sprinkle the reserved cheese over the top, then pour 1/2 cup whole milk or half-and-half and 1/2 cup low-sodium chicken broth evenly over the potatoes.

6-Cover the skillet tightly with foil, seal the edges, and bake for 50 minutes to let the flavors meld.

7-Remove the foil and bake for an additional 15-20 minutes until the potatoes are tender and the top turns golden. Let it cool slightly before serving hot. Preparation takes around 30 minutes, with total baking time of about 1 hour and 45 minutes.