This Savory Rainbow Sweet Potatoes au Gratin with cheddar rosemary sauce proves that sweet potatoes don’t always have to be covered in brown sugar & pecans.
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Can you taste the rainbow?
I love the many colors that potatoes and sweet potatoes come in. You’ve got the basic Idaho white potatoes and red potatoes, which are only red on the outside. Then you’ve got your Yukon golds and purple majesties.
Moving into the sweet potato family, there is also a white version popular in Korea and purple varieties called Okinawa and Ube. Plus, the orange sweet potatoes we all crush on during Thanksgiving.
Fortunately, more and more of these varieties are showing up in our local markets.
Ingredients
- Sweet Potatoes: You can make this recipe for sweet potatoes au gratin with any trio of colors. If you can’t find white sweet potatoes, use a Yukon gold. Can’t find ube, use the purple majesties.
- All-Purpose Flour
- Butter: Unsalted butter or salted butter are both fine.
- Cheese: White cheddar cheese, Fontina cheese or gruyere cheese.
- Fresh Herbs: I usually just use rosemary, but you can also add fresh thyme.
- Kosher Salt and Black Pepper
- Nutmeg: I recommend grating it freshly for the richest flavor.
- Heavy Cream
- Milk
SUBSTITUTIONS: Instead of heavy cream and milk, you can also use half and half.
How to prep the sweet potatoes
- STEP ONE: To get things started, give the potatoes a good scrub to clean them, and then slice them into 1/8-inch slices. There’s no need to peel them.
PRO TIP: I highly recommend using a mandoline. It will speed up prep time tremendously, and will guarantee even slices.
- STEP TWO: Once everything is sliced, create 2-3-inch tall stacks, alternating the colors. It’s okay if the slices aren’t evenly sized. We’ll adjust that when we move them to the pan.
- STEP THREE: When your stacks are built, carefully transfer the sliced potatoes layers into a greased cast iron skillet or baking dish.
- STEP FOUR: Build the outer circle first. Then, create the inner circle. If you notice that some colors aren’t shining through, lift them up, so they can be seen. If some of your slices are super small, you can fit two slices in there, so one boosts up the other.
Making the cheese sauce
This dish can be paired with any type of cheese. If you’re using all or mostly sweet potatoes, I recommend choosing a cheese variety that goes well with fruit. Think about it. Sweet potatoes are sweet, like fruit, so it just makes sense.
I chose a nice Vermont cheddar, which pairs wonderfully with apple and pears, but a fontina would also be nice. I do recommend selecting a white cheese instead of a yellow cheese, so the colors of the potatoes really pop.
The cheese sauce is made by creating a light roux of butter and flour. Then, add in the fresh rosemary, salt and pepper, and a dash of nutmeg. Nutmeg takes all cream sauces to the next level.
Whisk in the cream and milk, until you have a velvety smooth sauce. Then take the pan off the heat and stir in your shredded cheese.
Drizzle that magic cream sauce over the potatoes and bake it in the oven or smoker.
The results are a true showstopper, so much so that this side might outshine the entree.
How to serve au gratin
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Storage
Store leftover sweet potatoes au gratin in the fridge in an airtight container. It will last for up to a week. You can also freeze leftovers for several months.
GCG Pro Pitmaster Tips
- Choose a variety of colors for the move vibrant results
- Use a mandolin for even thickness
- Alternate colors and lift up smaller pieces so they show through
- Use white cheddar cheese for color contrast
More Sweet Potatoes Recipes
- Irresistible Sweet Potato Casserole with Praline Pecans
- Chorizo Hot Maple Grilled Sweet Potatoes
- Grilled Sweet Potatoes with Roasted Marshmallows
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Savory Rainbow Sweet Potatoes Au Gratin
Ingredients
- 1 white sweet potato
- 1 yellow sweet potato (yam)
- 1 purple sweet potato
- 3 tbsp flour
- 3 tbsp butter
- 1 tsp fresh rosemary, minced
- 1/2 tsp kosher salt
- 1/2 tsp fresh ground black pepper
- pinch nutmeg
- 1 cup heavy cream
- 1 cup milk
- 1 cup white cheddar cheese, shredded
Instructions
- Heat oven or smoker to 400F degrees.
- Slice each potato into 1/8-inch slices.
- Stack the potatoes into 2-3-inch stacks, alternating potato colors.
- Grease a round baking dish or cast iron pan.
- Transfer the potato stacks to the pan, laying them on their sides and creating an outer and inner circle.
- In a sauce pot, melt the butter over medium heat. Whisk in the flour. Cook for three minutes, whisking occasionally. Add the rosemary, salt, pepper and nutmeg.
- Whisk in the cream and milk. Continue whisking, until it starts to thicken.
- Remove the pan from the heat, and whisk in the cheese.
- Pour the sauce over the potatoes. Cover with foil, and place on a sheet pan.
- Bake in a 400F-degree oven or smoker for one hour. Remove the foil, and bake 20-30 more minutes, or until the cheese begins to brown and bubble.
Nutrition
Nutrition information is automatically calculated, so should only be used as an approximation.
How could I make this gluten free?
You can use gluten-free flour instead of all-purpose flour.
I am excitedly looking forward to serving this at Christmas Eve. Do you have any suggestions for how to make ahead by 1 day?
So sorry I didn’t see this sooner. I think you could layer everything, chill and then cook the next day.