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A creamy potato gratin in an oval baking dish, topped with fresh herbs and a metal serving spoon.

The Last Au Gratin Potatoes Recipe You’ll Ever Need

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  • Author: Jess Larson
  • Prep Time: 20 minutes
  • Cook Time: 1 hour, 30 minutes
  • Total Time: 1 hour, 50 minutes
  • Yield: 10-12 servings 1x
  • Category: Side Dishes, Thanksgiving Recipes, Christmas Recipes
  • Method: Baking
  • Cuisine: French
  • Diet: Gluten-Free

Description

This is it: the last Au Gratin Potatoes recipe you’ll ever need!

Buttery Yukon Gold potatoes slowly bake in a thyme-infused cream sauce with thinly sliced leeks, melty Gruyère, and Parmesan cheese, then finish bubbly and golden on top.

Inspired by the special-occasion potatoes my mom made for every holiday meal throughout my childhood, I’ve tested this treasured family recipe until every bite is perfectly tender, creamy, and deeply savory. A foolproof potato casserole and side dish made for Christmas, Thanksgiving, and cozy Sunday suppers.

Ingredients

Scale
  • 3 pounds Yukon Gold potatoes, sliced ⅛-inch thick
  • 2 small leeks, cleaned and thinly sliced (about 1 heaping cup)
  • 12 ounces good-melting cheese (I love Gruyère, smoked gouda, or comte), freshly shredded (about 3 cups)
  • 1 ¼ cups finely grated Parmesan cheese, divided
  • kosher salt and black pepper, to season
  • very soft butter, for greasing the pan

for the thyme cream:

  • 3 ½ cups heavy cream
  • 10 cloves garlic, smashed and roughly chopped
  • 3 tablespoons fresh thyme leaves

Instructions

METHOD OVERVIEW

Steep cream with garlic and thyme. Toss sliced potatoes, leeks, shredded cheese, about ⅓ of the Parmesan, salt, pepper, and the warm cream. Layer the mixture into a buttered casserole dish, finishing with a layer of potatoes (rather than leeks) and spooning any extra cream over top. Bake covered 60 minutes, then uncover, top with reserved Parmesan, and bake 20-30 minutes longer until golden brown and tender. Let cool slightly, then serve straight from the pan.

STEP-BY-STEP INSTRUCTIONS

  1. Prep the oven and pan: Preheat the oven to 400 degrees F, ensuring a rack is positioned in the center of the oven. Generously butter (or coat with nonstick cooking spray) the base and sides of a 9×13-inch pan (I use a 4-qt casserole dish) and set aside.
  2. Steep the thyme cream: In a small saucepan, combine the heavy cream, garlic, and thyme. Bring to a gentle simmer over medium heat and cook 4-5 minutes, just until fragrant. Remove from the heat and set aside to steep while you prepare the remaining ingredients.
    Cream being poured into a saucepan containing chopped garlic and fresh thyme sprigs.
  3. Meanwhile, prep the potatoes and leeks: Thinly slice the potatoes about ⅛-inch thick. A mandoline is helpful here for evenly thin slices, though a sharp knife works as well. Trim, clean, and thinly slice the leeks.
    Sliced potatoes and chopped leeks on a wooden cutting board with a mandoline slicer.
  4. Build the potato mixture: Add the sliced potatoes, leeks, shredded cheese, and ½ cup of the Parmesan to a large bowl. Season with a scant 1 teaspoon kosher salt and a few twists of black pepper. Pour the warm thyme cream over the mixture and toss well with your hands, separating any potato slices that are sticking together so the cream evenly coats everything.
    A glass bowl filled with sliced potatoes, leeks, and a creamy sauce, surrounded by small dishes of grated cheese, salt, and pepper.
  5. Assemble the gratin: Transfer the potato mixture to the prepared baking dish, arranging it in even layers. It’s best to finish with a layer of potatoes on top (rather than leeks). Spoon any extra cream from the bowl evenly over the assembled gratin. It’s okay if this gets a little messy – just wipe any drips from the pan before baking to prevent burning.
    An oval baking dish filled with thinly sliced potatoes, leeks, and a creamy sauce, surrounded by bowls of grated cheese, salt, and a piece of Parmesan.
  6. Bake the au gratin potatoes: Cover the baking dish tightly with foil and transfer to the oven. Bake covered for 60 minutes. Remove the foil and sprinkle the remaining ¾ cup Parmesan over the top. Return to the oven and bake uncovered 20-30 minutes longer, until the top is golden brown and the potatoes are tender when pierced with a fork.
    A hand sprinkles grated cheese over a baked potato gratin in an oval casserole dish.
  7. Serve: Allow the au gratin potatoes to cool 10-15 minutes so the cream begins to set, then serve warm.
    A serving spoon lifting a portion of cheesy au gratin potatoes topped with fresh thyme.

Equipment

Notes

  • Potatoes: Yukon Gold potatoes are my favorite for au gratin. Compared to starchier varieties like Russets, Yukon Golds have a naturally buttery flavor and creamy texture that becomes perfectly tender as they bake. Plus, their thin skins mean there’s no need to peel them. For best results, use a mandoline to slice the potatoes evenly to about ⅛-inch thick so they cook at the same rate.
  • Storage and Reheating: Leftover au gratin potatoes will keep, stored in an airtight container in the refrigerator, for up to 4 days. Reheat in the microwave or in a 350 degree F oven or air fryer until warmed through. The air fryer is my favorite – it revives the golden edges beautifully while keeping the potatoes creamy and tender.

Nutrition

  • Serving Size:
  • Calories: 587
  • Sugar: 4.5 g
  • Sodium: 571.8 mg
  • Fat: 44 g
  • Saturated Fat: 27.4 g
  • Trans Fat: 1 g
  • Carbohydrates: 30.4 g
  • Fiber: 3.4 g
  • Protein: 19.6 g
  • Cholesterol: 138.8 mg

Find it online: https://playswellwithbutter.com/au-gratin-potatoes/