Cast-Iron Potatoes au Gratin

Is there anything more comforting than layers of thinly sliced potatoes bathed in creamy goodness and topped with a golden, bubbly crust?

This cast-iron potatoes au gratin combines the earthy sweetness of sweet potatoes with buttery Yukon golds for a side dish that steals the spotlight at any meal.

What makes this version special is the marriage of two potato varieties and the magic of herbs and cheese.

The cast iron skillet isn’t just for show—it creates those perfectly crispy edges while keeping the center tender and creamy.

Plus, using both sweet potatoes and Yukon golds creates a beautiful visual contrast and complex flavor that elevates this from basic side dish to dinner table masterpiece.

Ingredients

For the potato base:

• 3 medium sweet potatoes
• 6 small Yukon gold potatoes
• 1 teaspoon kosher salt
• ¼ teaspoon ground black pepper
• ¾ teaspoon garlic powder
• 1½ teaspoons dried parsley
• ½ teaspoon dried thyme
• ½ teaspoon dried sage
• ½ teaspoon dried rosemary

For the creamy elements:

• 8 ounces Gruyère or sharp white cheddar, grated (2 cups)
• ½ cup thinly sliced yellow onion, chopped
• ½ cup whole milk or half-and-half
• ½ cup low-sodium chicken broth

Steps

1. Preheat your oven to 375°F (190°C). This moderate temperature allows the potatoes to cook through without burning the cheese on top. Ensure your rack is positioned in the middle of the oven for even heat distribution.
2. Peel both the sweet potatoes and Yukon gold potatoes. Using a mandolin or vegetable slicer, cut all potatoes into very thin slices, approximately ⅛-inch thick. A mandolin is strongly recommended here—hand-cutting rarely achieves the consistent thinness needed for proper cooking.
3. In a large bowl, gently toss the potato slices with 1 teaspoon kosher salt, ¼ teaspoon black pepper, ¾ teaspoon garlic powder, 1½ teaspoons dried parsley, ½ teaspoon dried thyme, ½ teaspoon dried sage, ½ teaspoon dried rosemary, all of the grated cheese, and the ½ cup chopped onion. Use your hands or a flexible spatula to mix everything evenly without breaking the delicate potato slices. The goal is to coat each slice with seasonings and distribute the cheese and onions throughout.
4. Working with small handfuls at a time, arrange the coated potato slices in a 10-inch cast-iron skillet or 2-quart baking dish. You can create neat rows or a more rustic arrangement—both work beautifully. For the most impressive presentation, alternate sweet potato and Yukon gold slices in visible top layers.
5. Once all potatoes are arranged, pour the ½ cup milk (or half-and-half) and ½ cup chicken broth evenly over the potatoes. The liquid should come about halfway up the sides of the potatoes—not completely submerge them.
6. Cover the pan tightly with aluminum foil, making sure to seal around all edges. This creates a steamy environment that helps cook the potatoes through before browning begins.
7. Bake covered for 50 minutes. The potatoes need this time to become tender throughout—rushing this step will result in undercooked, crunchy potatoes.
8. After 50 minutes, carefully remove the foil (watch for hot steam!). Continue baking uncovered for 15-20 more minutes until the top is golden brown and bubbling around the edges. The exposed edges of potatoes should look crispy, and you should see active bubbling around the sides of the dish.
9. Test for doneness by inserting a knife into the center of the dish—it should slide through the potatoes with no resistance. If you encounter any firmness, continue baking for 5-minute intervals until completely tender.
10. Remove from the oven and allow to cool for 10-15 minutes before serving. This resting period allows the sauce to thicken slightly and makes serving neater. The dish will be extremely hot, especially in cast iron which retains heat exceptionally well.

Smart Swaps

• Replace half-and-half with evaporated milk (1:1 ratio) for fewer calories but similar creaminess
• Substitute smoked Gouda for the Gruyère to add a subtle smoky dimension
• Use fresh herbs instead of dried (triple the amounts) for brighter flavor in summer months
• Replace chicken broth with vegetable broth for a vegetarian version

Make It Diabetes-Friendly

• Reduce carbs by using all Yukon gold potatoes instead of sweet potatoes (saves approximately 7g carbs per serving)
• Replace half the potatoes with thinly sliced turnips or rutabaga to cut carbs by 40% per serving
• Use unsweetened almond milk instead of whole milk to save 6g carbs per recipe
• Add 1 tablespoon of ground flaxseed to the mix to improve the glycemic response
• Serve a ½ cup portion (approximately 15g net carbs) alongside protein to reduce blood sugar impact

Pro Tips

• Slice potatoes directly into cold water to prevent browning, then pat completely dry before seasoning
• For extra crispy edges, butter the inside of your cast iron skillet before adding potatoes
• Let the assembled dish rest for 15 minutes before baking to allow the seasonings to penetrate the potatoes
• For a make-ahead version, assemble everything but don’t add the liquid until just before baking
• The leftovers actually improve overnight as flavors meld—reheat in a 350°F (175°C) oven for 15-20 minutes