We are talking calorie-busting decadence here, but oh so worth it! Just keep in mind, a little goes a long way—think French when considering portion size; after all, Gruyère cheese is in the gratin. And it was a perfect accompaniment to our main course of sous vide, pan-seared beef tenderloin, which in of itself is very lean.
The Hubs and I were a bit leery about the seemingly low amount of liquid, but it turned out perfectly creamy. One of our dinner guests admitted to disliking celery immensely and was concerned when he heard it contained celery root. However, he loved the gratin, even taking seconds!
A mandoline comes in real handy for uniformly-thin slices of potatoes and celery root. To aid in scheduling your dinner, this gratin can be made up to two hours ahead of time, covered with foil, then reheated for about 20 minutes.
Preheat to 350°. Heat cream, garlic, and thyme sprig in a medium saucepan just until bubbles begin to form around edge of pan. Remove from heat; set aside to steep.
Melt 1 tablespoon butter in a medium skillet over medium heat. Add leeks; season with salt and cook, stirring often, until tender (do not brown), 10–12 minutes. Transfer to a small bowl and set aside.
Butter a 3-quart gratin dish with remaining 1 tablespoon butter. Layer 1/3 of potato slices and 1/3 of celery root slices evenly over bottom of baking dish. Cover with 1/3 of leeks, then 1/3 of Gruyère. Sprinkle with salt, pepper, and 1 teaspoon thyme leaves. Repeat layers twice more. Strain cream mixture into a medium pitcher and pour over vegetables.
Set gratin dish on a large rimmed baking sheet and cover tightly with foil. Bake for 1 hour. Carefully remove foil; continue baking until top is golden brown and sauce is bubbling, 25–30 minutes. DO AHEAD: Can be made 2 hours ahead. Let stand at room temperature. Tent with foil and rewarm in a 300° oven until hot, about 20 minutes.
This rich, creamy gratin gets a note of smokiness from the bacon between the layers of tender potatoes. A hand mandoline positioned over a large bowl makes an excellent tool for which to create perfectly sized potato slices.
Definitely company-worthy and impressive, not to mention sinfully decadent and flavorful, these were a big hit for all of us.
3 medium leeks, white and light-green parts only, thinly sliced
6 oz. grated Gruyère
1 Tbsp. chopped fresh thyme
1/4 tsp. freshly grated nutmeg
1/2 cup fresh breadcrumbs
1/4 cup finely grated Parmigiano-Reggiano
2 Tbs. unsalted butter, melted
Sweet paprika, for topping (optional)
Position a rack in the center of the oven and heat the oven to 400°F. Butter or oil a 3-quart gratin dish; set aside.
Put the potatoes, cream , 1/2 tsp. salt, and a few grinds of pepper in a 12-inch skillet. Simmer, partially covered, over medium to medium-low heat, stirring often and gently with a rubber spatula until the potatoes are barely tender when pierced with a fork or skewer, 8 to 12 minutes.
In a medium skillet, cook the bacon until browned and fully cooked. Set aside to cool, reserving 2 Tbs. of the fat in the skillet. Heat the reserved fat over medium-high heat and sauté leeks until tender, fragrant, and lightly browned. Season to taste with salt and pepper. When the bacon is cool, crumble it into small pieces.
Using a slotted spoon, transfer half the potatoes to the prepared gratin dish, spreading them evenly. Layer on the leeks, bacon, Gruyère, thyme, and nutmeg. Top with the remaining potatoes spreading them evenly, and pour over any liquid remaining in the pan.
In a small bowl, combine the breadcrumbs, Parmigiano-Reggiano, and melted butter. Evenly scatter the topping mixture over the potatoes. If using, sprinkle a light layer of sweet paprika over the breadcrumb topping.
Bake the gratin until it’s bubbly, the top is brown, and the potatoes are completely tender when poked with a fork or a skewer, 25 to 30 minutes. Let the gratin sit for at least 10 and up to 30 minutes before serving so the liquid is fully absorbed and the layers are cohesive.