A classic potato au gratin is a beloved holiday side, rich and creamy—and usually loaded with cheese. This version keeps the comforting texture and deep flavor but makes it dairy-free and compliant with Whole30 and Paleo approaches. Thinly sliced potatoes layered with softened leeks and onions are baked in a savory, coconut-based cream sauce until tender and golden. The result is a hearty, elegant side dish that stands up to a holiday table or any special meal, without relying on dairy.
Potatoes sliced very thin, a fragrant sauté of onions and leeks, garlic, and a silky coconut-chicken sauce come together into a gratin that’s creamy and satisfying. If you’re used to cheesy gratins, this recipe proves you don’t need dairy to achieve richness and depth of flavor. It’s a great option for guests who avoid dairy, and it doubles well for meal prep.
For best results, slice the potatoes as thinly and evenly as possible. A mandoline is ideal for getting paper-thin slices quickly and consistently; if you don’t already own one, it’s a useful tool for holiday cooking and for preparing vegetables throughout the year. Alternatively, a very sharp knife and patient hands will work.
Make this Whole30/Paleo Potato-Leek Au Gratin for a healthier holiday centerpiece or an elevated side dish any time you want comforting, dairy-free potatoes. Below you’ll find the full ingredient list, clear instructions, and helpful tips for success.
- 3 lbs large yellow potatoes
- 1/2 large yellow onion, sliced very thinly
- 2 leeks, white and light green parts only, cleaned and sliced thin
- 2 cloves garlic, minced
- 2 tbsp olive oil
- 1 tbsp ghee
- Cooking spray (or a light brushing of ghee)
- 2 tbsp ghee
- 2 cloves garlic, minced
- 1 cup full-fat canned unsweetened coconut milk (stir or blend before measuring)
- 1 cup chicken broth
- 1 tbsp arrowroot starch
- Salt and freshly ground black pepper, to taste
- 4 sprigs fresh thyme, leaves removed
- Aluminum foil
- Preheat the oven to 350°F (175°C).
- Peel the potatoes. Using a mandoline or a sharp knife, slice the potatoes to about 1/8 inch thickness and set aside.
- Heat 2 tablespoons olive oil and 1 tablespoon ghee in a skillet over medium-high heat. Add the sliced leeks, sliced onion, and 2 cloves minced garlic. Season with salt and pepper and sauté until the vegetables are very tender, about 5–7 minutes. Remove from heat.
- In a large bowl, combine the sautéed onions and leeks with the sliced potatoes. Toss gently to coat and season with additional salt and pepper as needed.
- Lightly grease a casserole dish with cooking spray or ghee. Arrange the potato and onion mixture evenly across the dish in a single or slightly overlapping layer.
- To make the sauce, melt 2 tablespoons ghee in a skillet over medium heat. Add the garlic and sauté briefly for 30 seconds to 1 minute until fragrant but not browned. In a small bowl, whisk the chicken broth with 1 tablespoon arrowroot starch until smooth. Pour the broth mixture and 1 cup coconut milk into the skillet and whisk to combine.
- Add the fresh thyme leaves and season with salt and pepper. Let the sauce simmer gently for about 5 minutes, stirring often, until it thickens slightly.
- Pour the warm sauce evenly over the layered potatoes in the casserole. Cover tightly with aluminum foil and bake at 350°F for 40 minutes. Remove the foil and bake an additional 15 minutes uncovered. If the top hasn’t developed a golden color, switch the oven to broil and broil for 3–5 minutes, watching closely to prevent burning.
- Remove from the oven and allow the gratin to rest for 10–15 minutes before serving. This resting time helps the sauce thicken and the layers set, yielding neatly sliced portions.
- Serve and enjoy warm. This gratin pairs beautifully with roasted meats, poultry, or a hearty vegetable main.
- For even cooking, try to keep potato slices uniform. A mandoline speeds this up and delivers reliable results.
- Swap chicken broth for vegetable broth to make the dish vegetarian-friendly (but not Whole30 compliant if you use non-compliant ingredients).
- Add a handful of chopped fresh herbs such as parsley or chives after baking for brightness.
- Leftovers store well in the refrigerator for 3–4 days. Reheat gently in the oven to retain texture.