Easy and Sweet Potato Gratin with Cream and Thyme is a simple, comforting dish featuring thinly sliced sweet potatoes baked in creamy, flavorful sauce with fresh thyme. The edges get beautifully golden and a little crispy while the inside stays tender and rich. It’s a lovely balance of sweet, creamy, and herb-y that feels just right, especially on colder nights.
I like making this gratin when I need something cozy but don’t want to spend too much time in the kitchen. The fresh thyme adds such a nice touch of earthiness that brightens up the natural sweetness of the potatoes, and the cream keeps each bite smooth and satisfying. I often sneak a taste while it’s baking because it smells so good! A little tip I’ve learned is to slice the sweet potatoes evenly so everything cooks at the same pace and turns out perfectly soft.
This dish is a wonderful side for just about any meal, but my favorite way to serve it is alongside roasted chicken or a simple green salad for a well-rounded dinner. It’s also great for gatherings since you can prepare it ahead and pop it into the oven when guests arrive. I always get compliments on it, and it warms me up just thinking about it. Sweet potato gratin feels like a little hug on a plate!
Key Ingredients & Substitutions
- Sweet Potatoes
- These add natural sweetness and creaminess. If you want less sweetness, use all Yukon gold potatoes or mix them as in the recipe. Always peel and slice them evenly for even cooking.
- Potatoes (Yukon Gold or Russet)
- Yukon golds are creamy and rich, while Russets hold their shape well. You can use just one type if preferred or swap with fingerlings for a different texture.
- Cream & Milk
- Heavy cream makes the gratin rich and smooth, while milk lightens it up a bit. You can substitute half-and-half for a lighter version or use all cream for extra richness.
- Garlic & Thyme
- Fresh garlic and thyme are simple but add big flavor. Thyme gives a nice herb aroma, but rosemary or sage work well too if you don't have thyme. Dried herbs can be used at half the amount.
- Cheese
- Gruyère melts beautifully with a nutty flavor. Parmesan offers a sharper note. You can swap with cheddar, mozzarella, or fontina depending on your taste or what you have on hand.
How Can I Make Sure the Potatoes Cook Evenly and Don’t Turn Mushy?
Even slicing and layering are key to the perfect gratin. Here’s how to get it right:
- Slice Thinly: Use a mandoline or sharp knife to slice potatoes about 1/8 inch thick. Thin slices cook faster and more evenly.
- Alternate Layers: Mix sweet potatoes with regular potatoes in layers to balance textures and flavors.
- Use Warm Cream: Pouring warm cream over layers helps kick-start cooking and keeps things cozy inside the dish.
- Cover While Baking: Start with foil to trap moisture, then remove it later to brown the top.
- Check Doneness: Test by piercing the potatoes with a knife; it should slide in easily but the slices should still hold their shape.
Following these tips will help you get tender, creamy potatoes with a golden top—not mushy and runny. I always find a little patience during baking makes all the difference!
Equipment You’ll Need
- Baking dish (9×13 inch or similar) – holds the gratin nicely and lets it cook evenly.
- Mandoline or sharp knife – for slicing potatoes thin and evenly, so they cook well.
- Medium saucepan – to warm the cream mixture and gently infuse flavors.
- Aluminum foil – to cover the dish while baking, keeping moisture in for tender potatoes.
- Grater – for shredding cheese evenly, helping it melt smoothly on top.
- Wooden spoon or spatula – for layering the potatoes and cream without breaking slices.
Flavor Variations & Add-Ins
- Add cooked, crumbled bacon or pancetta for a smoky salty kick that pairs well with the sweet potatoes.
- Mix in thinly sliced leeks or caramelized onions for a mild, sweet onion flavor to deepen the dish.
- Use fresh rosemary instead of thyme for a pine-like aroma that changes the herb profile.
- Sprinkle nutmeg or cayenne pepper into the cream for warm spice or gentle heat, especially cozy in cooler months.
Easy and Sweet Potato Gratin with Cream and Thyme
Ingredients You’ll Need:
For the Potatoes:
- 3 large sweet potatoes, peeled and thinly sliced
- 2 large Yukon gold or Russet potatoes, peeled and thinly sliced
For the Cream Mixture:
- 2 cups heavy cream
- 1 cup whole milk
- 3 cloves garlic, minced
- 1 teaspoon fresh thyme leaves (plus extra for garnish)
- Salt and freshly ground black pepper, to taste
- Optional: pinch of nutmeg
For the Topping and Preparation:
- 1 ½ cups grated Gruyère or Parmesan cheese
- 2 tablespoons unsalted butter (for greasing the baking dish)
How Much Time Will You Need?
Prepare to spend about 15 minutes slicing and layering the potatoes and cream. Baking will take approximately 1 hour and 10 minutes total—45 minutes covered, then 20-25 minutes uncovered to get that perfect golden top. Allow about 10 minutes of resting time before serving to let it set.
Step-by-Step Instructions:
1. Preheat Oven and Prepare Baking Dish:
Heat your oven to 375°F (190°C). Grease a 9×13 inch baking dish with the unsalted butter so the gratin won’t stick later on.
2. Make the Cream Sauce:
In a medium saucepan over medium heat, combine the heavy cream, milk, minced garlic, fresh thyme, salt, pepper, and a pinch of nutmeg if you like. Warm it just until it starts to simmer, then remove from heat and set aside.
3. Layer the Potatoes and Cream:
Arrange a layer of the sliced potatoes in the bottom of the buttered dish, alternating sweet potatoes and regular potatoes to balance flavors and texture. Pour a little of the warm cream mixture over this first layer, just enough to lightly cover the potatoes. Sprinkle some grated cheese on top. Repeat layering potatoes, cream, and cheese until all ingredients are used, finishing with cheese on top.
4. Bake and Brown:
Cover the dish with aluminum foil to keep it moist, and bake for 45 minutes. Then, remove the foil and bake for another 20-25 minutes or until the top is golden brown and the potatoes are tender when pierced with a knife.
5. Rest and Serve:
Let the gratin rest for about 10 minutes after baking so it can thicken a bit and flavors blend. Garnish with extra fresh thyme leaves to brighten it up, and serve warm. Enjoy your creamy, delicious sweet potato gratin!
Can I Use Frozen Sweet Potatoes for This Gratin?
It’s best to use fresh sweet potatoes for this recipe because frozen ones tend to have excess moisture that can make the gratin watery. If you must use frozen, thaw them fully and pat dry before slicing and layering.
How Long Can I Store Leftovers?
Store any leftovers in an airtight container in the refrigerator for up to 3 days. Reheat gently in the oven or microwave, adding a splash of cream or milk if needed to restore creaminess.
Can I Make This Gratin Ahead of Time?
Absolutely! Assemble the gratin and cover it with foil, then refrigerate for up to 24 hours before baking. Just add a few extra minutes to the baking time if baking straight from the fridge.
What Can I Substitute for Gruyère Cheese?
If you don’t have Gruyère, Parmesan, Fontina, or a mild cheddar work great. Choose a cheese that melts well and complements the creamy texture without overpowering the delicate thyme and sweet potatoes.