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A square slice of layered potato gratin topped with golden breadcrumbs and herbs, served on a rustic, speckled beige plate.

Chili-Lime Pistachio Sweet Potato Gratin

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A creamy, spiced sweet potato gratin layered with crisp fried shallots and finished with Tajín-seasoned pistachios for a bright, crunchy topper.
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Prep Time 35 minutes
Cook Time 45 minutes
Total Time 1 hour 20 minutes
Servings: 6
Course: Holiday, Side Dish
Cuisine: Californian, Seasonal
Ingredients Equipment Method Notes

Ingredients
  

Sweet Potatoes
  • 2 lbs sweet potatoes peeled and sliced ⅛ inch thick on a mandoline
Cheese Sauce
  • kosher salt to taste
  • 1 tablespoon fresh thyme roughly chopped
  • 4 oz Parmesan cheese shredded
  • 4 oz Gruyère cheese freshly grated
  • 4 oz Sharp Cheddar cheese freshly grated
  • ¼ cup milk
  • 1 cup heavy cream
  • 2 tablespoon butter
  • 2 cloves garlic
  • ¼ teaspoon nutmeg
  • ¼ teaspoon red pepper flakes
Fried Shallots
  • 2 shallots thinly sliced
  • Avocado oil enough for frying
To Finish
  • ½ bag Tajín Seasoned Pistachios
  • 2 oz Parmesan freshly grated
  • ¼ cup chives thinly sliced

Equipment

  • Mandoline
  • Cast iron skillet or baking dish
  • Medium saucepan
  • Small saucepan
  • Food processor
  • Foil
  • Oven

Method
 

Fry the Shallots
  1. Preheat the oven to 375F and lightly grease a cast iron skillet or baking dish.
  2. In a small saucepan, add 3 inches avocado oil over medium heat. Once hot (350–375F), add shallots and fry until just turning golden. You'll know they're ready when they're light amber and the bubbling quiets. Transfer to a paper towel-lined plate and season immediately with kosher salt.
  3. Set aside.
Make the Cheese Sauce
  1. Melt butter in a medium saucepan over medium heat.
  2. Add garlic and cook until fragrant (~1 minute).
  3. Add milk, cream, thyme, nutmeg, red pepper flakes, and salt. Bring to a gentle simmer. You're looking for a bare simmer: small bubbles breaking the surface, not a rolling boil.
  4. Reduce heat to low and cook 10–12 minutes to reduce.
  5. Remove from heat and stir in Gruyère and cheddar until smooth.
  6. Season to taste.
Assemble
  1. Sprinkle ⅔ of the fried shallots in an even layer in the baking dish.
  2. Add ⅓ of the cheese sauce.
  3. Add a layer of sweet potatoes.
  4. Add remaining shallots and another ⅓ of the cheese sauce.
  5. Add remaining sweet potatoes and top with remaining cheese sauce.
  6. Tap the dish gently to settle the sauce.
  7. Cover with foil and bake 45 minutes.
Finish
  1. Remove foil and bake uncovered 15 minutes.
  2. Pulse half a bag of Tajín Seasoned Pistachios in a food processor until coarse.
  3. Sprinkle pistachios over the gratin, followed by the grated Parmesan.
  4. Return to the oven for 5 minutes or broil briefly until golden.
  5. Rest 10 minutes before serving.
  6. Garnish with chives.
To Plate
  1. Scoop directly from the dish or slice into portions. Finish with chives.

Notes

Storage: cover and refrigerate the gratin for up to 4 days. Reheat covered in a 350°F oven until hot in the center, then uncover for a few minutes to bring the top back. Add fresh pistachios after reheating so they stay crunchy.
Leftover sweet potato slices can be fried in the shallot oil for quick sweet potato chips.

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