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These sourdough au gratin potatoes are the ultimate comfort food side dish. Thinly sliced potatoes are coated in a rich homemade cheese sauce made with sharp cheddar, Gruyere, fresh garlic, and sourdough discard before baking until golden and bubbling. It’s the perfect dish to feed a crowd, and if my family is any indication, I’m guessing your guests won’t be able to stop eating it!
Why You’ll Love This Recipe
- Rich, Creamy, and Decadent – If you love comforting side dishes like sourdough mac and cheese, you’re going to love these potatoes too. The sourdough starter adds a lovely subtle tang that really elevates this dish to the next level.
- Simple to Make – You’re making a cheese sauce with sourdough starter, mixing it with potatoes, and baking – that’s it! Using sourdough starter to thicken a sauce is so simple, and if you use a food processor to slice the potatoes and grate the cheese, it’s even easier.
- Perfect Way to Use Up Potatoes – If you ever find yourself with surplus potatoes in the house, make this! Not only does it use up so many potatoes, but it uses up 120 grams of sourdough discard.
Ingredients
- Butter – I always use salted butter, as I mention inside the Pantry Mama test kitchen, but feel free to use unsalted.
- Garlic cloves – Fresh garlic gives this sourdough potato dish incredible flavor!
- Sourdough Starter or Discard – Either one is fine for this dish.
- Heavy Cream – I prefer mostly cream in this dish for classic au gratin potatoes, but I’ll sometimes add in a bit of half-and-half or whole milk if I don’t have quite enough cream, and it works fine too.
- Cheddar and Gruyere – I use a mix of cheeses here, a nice sharp cheddar and a nutty Gruyere. If you’re using different cheeses, I would recommend having at least half or three-quarters of the cheese be a fairly standard melting cheese, such as cheddar, but feel free to choose another flavorful cheese such as Parmesan or even Brie for the remainder.
- Fresh Thyme – Adds a lovely flavor, but you can leave it out if you don’t have any.
- Salt and Freshly Ground Black Pepper
- Thinly Sliced Potatoes – I like a starchy potato here, like a Yukon Gold or russet. Slice them thin using a food processor or mandoline. I don’t peel my potatoes because I like the look and texture of the browned edges. Plus peeling them is a pain, but feel free to peel your potatoes if you’d like.
How To Make Sourdough Au Gratin Potatoes
Start by preheating the oven to 375ºF/180ºC. Grease a 9×13-inch casserole dish – I use butter.
First up, make the delicious creamy cheese sauce. You need to melt some butter over a medium heat, adding garlic and then mixing in the sourdough starter, stirring frequently until the sauce becomes golden brown. This generally takes around 3 to 5 minutes depending on your stove top.
Slowly pour in the cream, whisk to combine, and cook until the cream sauce is warm and thick. Stir in about 3/4 of the cheddar and Gruyere (reserve the rest for topping the potatoes) as well as the thyme leaves, salt, and a few grinds of black pepper. Stir until most of the cheese has melted and the sauce is fairly smooth.
If there are still a few lumps, it’s not the end of the world, but try to whisk it enough that’s pretty smooth and pourable.
Next you’ll combine the potatoes and the sauce. I find the easiest way to get all the potatoes coated is to use a large bowl. I like to split the potatoes and sauce in two batches to make sure I can mix everything without spilling. Gently stir so all the potato slices get nicely covered in sauce.
Transfer the cheesy potatoes to the prepared baking dish. Try to keep the potatoes fairly even on top so the dish cooks evenly. Cover the dish with aluminum foil with a few holes in the top for steam to escape. Bake for 60 to 75 minutes, or until the potatoes are fork-tender all the way through.
Remove the foil and scatter the remaining cheddar and Gruyere over the top of the potatoes. Bake for about 10 to 15 minutes longer, or until the top is golden and bubbling and smells incredible. Let the dish stand a few minutes before serving. This is key for ensuring you get a thick, creamy sauce. Plus it makes it more pleasant to eat when you’re not burning the roof of your mouth!
Kate’s Pro Tip
Make Ahead
If you want to make these sourdough au gratin potatoes ahead of time, the best way to do this is to make the dish as normal but reserve about 1 cup of the creamy cheese mixture as well as the cheese for topping. Bake the dish with foil on until the potatoes are cooked through, let cool completely, pour the reserved creamy sauce on top, then refrigerate. When you’re ready to reheat, bake in a 350ºF/180ºC oven with the foil still on until the dish is warm throughout, 20 to 30 minutes, then scatter the cheese and bake until the cheese is golden and bubbling.
What To Serve With Sourdough Au Gratin Potatoes
These creamy potatoes pair beautifully with just about any hearty main course. I love serving them for Thanksgiving or Christmas alongside sourdough green bean casserole and plenty of sourdough gravy.
They’re also delicious with roast chicken, baked ham, or steak for a comforting Sunday dinner. If you’re building the ultimate comfort food meal, add a basket of sourdough dinner rolls.
How To Store + Freeze
This dish of Sourdough Au Gratin Potatoes will keep for 3 to 4 days in the fridge. You can reheat in the oven, but it can take some time as the potatoes are quite dense, so I usually just microwave to reheat and get a nice melt on the cheese.
The leftovers can be frozen, although cream-based dishes can separate or become grainy when frozen and thawed.
I’d recommend freezing in small portions, thawing overnight in the fridge, and reheating gently, and be prepared for a change in texture. You can also halve the recipe if you don’t think you’ll eat the entire baking dish.
Sourdough Au Gratin Potatoes
Equipment
- Baking Dish 9 x 13-inch
- Food Processor or mandoline, or sharp knife
- Large Mixing Bowl
- Medium Saucepan
Ingredients
- 50 g Butter
- 3 Garlic Cloves, (finely chopped)
- 120 g Sourdough Starter, (or discard)
- 650 g Heavy Cream, (or half-and-half or whole milk)
- 230 g Cheddar Cheese, (shredded)
- 120 g Gruyere Cheese, (shredded)
- 3 sprigs Fresh Thyme
- 5 g Salt
- Black Pepper, (freshly ground, to taste)
- 1.75 kg Potatoes, (approx. 4 lbs, thinly sliced)
Instructions
- Preheat the oven to 375℉/180℃ and grease a 9×13-in casserole dish.
- In a medium saucepan, melt the butter over medium heat. Add the chopped garlic and cook until the garlic is fragrant and softening, 1 to 2 minutes. Mix in the sourdough starter and cook until it turns a rich golden brown.
- Slowly pour in the cream, whisk to combine, and cook until the cream sauce is warm and thick. Stir in ¾ of the cheddar and Gruyere as well as the thyme leaves, salt, and a few grinds of black pepper. Stir until most of the cheese has melted and the sauce is fairly smooth.
- Next you’ll combine the potatoes and the sauce, ensuring all of the potato slices are evenly coated.
- Carefully transfer the cheesy potatoes to the prepared baking dish. Try to keep the potatoes fairly even on top so the dish cooks evenly. Cover the dish with aluminum foil with a few holes in the top for steam to escape. Bake for 60 to 75 minutes, or until the potatoes are fork-tender all the way through.
- Remove the foil and scatter the remaining cheddar and Gruyere over the top of the potatoes. Bake for about 10 to 15 minutes longer, or until the top is golden and bubbling and smells incredible. Let the dish stand a few minutes before serving.
Notes
- I don’t peel my potatoes because I like the look and texture of the browned edges. Plus peeling them is a pain, but feel free to peel your potatoes if you’d like.
- I prefer the texture of thinly sliced potatoes, so if you don’t have or want to use the food processor, you could also use a mandoline or a sharp knife.
- If your potatoes are going to sit out for a little while, soak them in a large bowl of cold water to prevent discoloration.
Nutrition
Nutrition information is automatically calculated, so should only be used as an approximation.
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