Name: Savory Sweet Potato, Oat & Sage Gratin with Cheese
Prep time: 15 min
Cook time: 55 min
Total time: 1 h 10 min
Cuisine: American
Ingredients: 3 medium sweet potatoes, peeled and thinly sliced; 1 cup rolled oats (not instant); 1 ½ cups grated sharp cheddar cheese (or any good melting cheese); 1 medium onion, thinly sliced; 2 tablespoons fresh sage, chopped; 1 clove garlic, minced; 2 tablespoons olive oil; 1 ½ cups milk (dairy or plant‑based); 1 tablespoon Dijon mustard; Salt and freshly ground black pepper to taste; 2 tablespoons grated Parmesan cheese (optional, for topping)

This Savory Sweet Potato, Oat & Sage Gratin with Cheese is a rich, layered dish that brings together earthy sweet potatoes, hearty oats, aromatic sage, and a golden cheesy crust. It’s rustic, satisfying, and perfectly suited for cozy fall or winter meals. Whether I’m serving it as a hearty vegetarian side or enjoying it as a main dish with a salad, it always hits the spot with its comforting flavors and creamy texture.

Why You’ll Love This Recipe

I love how this gratin balances both comfort and nourishment. The sweet potatoes offer natural sweetness and fiber, while oats bring a unique texture and heartiness I don’t usually find in a traditional gratin. The sage adds a woodsy aroma that plays so well with the sharp cheddar and creamy milk base. Plus, it’s easy to make ahead, perfect for holiday gatherings, or just a chilly night when I want something oven-baked and satisfying.

Ingredients

(Tip: You’ll find the full list of ingredients and measurements in the recipe card below.)

3 medium sweet potatoes, peeled and thinly sliced

1 cup rolled oats (not instant)

1 ½ cups grated sharp cheddar cheese (or any good melting cheese)

2 tablespoons fresh sage, chopped

1 medium onion, thinly sliced

1 clove garlic, minced

2 tablespoons olive oil

1 ½ cups milk (dairy or plant‑based)

1 tablespoon Dijon mustard

Salt and freshly ground black pepper to taste

2 tablespoons grated Parmesan cheese (optional, for topping)

Directions

I start by preheating the oven to 375°F (190°C) and lightly greasing a 9×9‑inch baking dish with olive oil.

In a skillet, I heat the olive oil over medium heat and sauté the onion and garlic until soft and fragrant—about 5 minutes. Then I stir in the chopped sage and let it cook for another minute.

I whisk together the milk and Dijon mustard in a bowl, seasoning it with salt and pepper.

I layer half the sweet potato slices in the dish, slightly overlapping them. Then I sprinkle half of the rolled oats, followed by half the onion-sage mixture and half the grated cheese.

Next I repeat the layers with the remaining ingredients, then pour the milk and mustard mixture evenly over everything.

I cover the dish with foil and bake it for 40 minutes. After removing the foil, I continue baking for another 15–20 minutes, until the top is golden and bubbling, and the sweet potatoes are fork-tender.

If I’m using Parmesan, I sprinkle it on during the last 5 minutes of baking for extra browning. I let it rest for 10 minutes before slicing and serving.

Servings and timing

Servings: 6

Prep Time: 15 minutes

Cook Time: 55 minutes

Total Time: 1 hour 10 minutes

Calories: ~360 kcal per serving

Variations

Make it vegan: I use plant-based milk and vegan cheese alternatives to make this fully plant-based.

Add greens: I’ve layered in sautéed spinach or kale between the potatoes for added nutrients.

Spice it up: A pinch of crushed red pepper or a dash of smoked paprika gives it a subtle kick.

Use other herbs: Thyme or rosemary can replace sage for a different aromatic profile.

Try different cheese: Gruyère, Fontina, or even blue cheese (in small amounts) changes the flavor in interesting ways.

Storage/Reheating

I store any leftovers in an airtight container in the fridge for up to 4 days. To reheat, I warm individual portions in the microwave or reheat the entire dish in the oven at 350°F (175°C) until hot throughout. It also freezes well—I just make sure to cool it completely before wrapping and freezing. I reheat frozen portions straight from the freezer or thaw overnight in the fridge first.

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FAQs

How do I know when the sweet potatoes are fully cooked?

I test by inserting a fork or knife into the center of the dish—if it slides through the sweet potatoes easily, they’re done. The top should also be bubbling and golden.

Can I prep this dish ahead of time?

Yes, I often assemble it completely, cover it, and store it in the fridge overnight. I then bake it just before serving—sometimes adding 5–10 extra minutes to the cooking time.

What type of oats work best?

Rolled oats are the best option here. I avoid instant oats, which can get mushy, and steel-cut oats, which don’t soften enough in this dish.

Can I add protein to make it a full meal?

Definitely. I’ve added cooked lentils, white beans, or shredded rotisserie chicken between the layers for a more protein-packed main dish.

Does this dish work as a holiday side?

Absolutely. It’s hearty, beautiful on the table, and pairs well with roasts, salads, and other holiday favorites. I always get compliments when I bring it to family dinners.

Conclusion

This Savory Sweet Potato, Oat & Sage Gratin with Cheese is one of those cozy, feel-good dishes I love turning to when the weather gets chilly. It’s flavorful, satisfying, and versatile enough for weeknight dinners or festive holiday meals. Whether I make it vegetarian or fully plant-based, it always delivers comfort in every bite.

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