If you were to pose that famous question to me, what would you choose for your last dinner, this would be on the menu for sure. The tender potatoes infused with the garlic and thyme and cream, the perfume of leeks that is the best compliment to potatoes there can be, and the crunchy, cheesy, butter topping give that oh so satisfying combination of gooey-cheesy-tender-crunchy that is the stuff of dreams.
This dish is just perfect.
We are having it with Bobby Flay’s Prime Rib and my mother-in-law’s famous Christmas sides which are delicious and easy – her Horseradish Carrots (so good it is the leftover you reach for first, and her Spinach Souffle.
I think with this gratin we will have the trifecta of sides and I am not sure what I am more excited for, the presents or the dinner.
Like so much good food, this dish starts with the simplest of ingredients. I once had to host Christmas last minute and had all of these on hand.
If you have a mandolin it makes the job of slicing the potatoes so easy. I like the skins on to provide a bit of body to the dish and because I don’t have to peel them. I used the 1/8 inch setting and love it, it ensures that it bakes through and gets soft and tender and you aren’t left with hard potatoes.
Once you have these sliced, you cut up the leeks taking care to remove any dirt between the layers. Then you arrange a layer of the potatoes, sprinkle with about a 1/3 of the cut leeks, then repeat making 3 layers depending on your pan. It’s pretty unfussy and rustic (read: easy) so don’t worry too much.
When you have done this, you heat two cups of cream in a sauce pan over medium heat, and add the garlic, thyme, salt and pepper. This heats quickly so watch it so it doesn’t scorch or boil over. Once the salt has dissolved, pour it evenly over the whole dish. 
Then you wrap it in foil, cook it for 30 min. at 350. Then you add the toppings:
Sprinkle the grated cheese all over it. Melt 2 tablespoons of butter and mix it with the panko and a pinch of salt and pepper. Sprinkle that over the top, and bake it uncovered for an additional 45 min.
The ingredients are so simple, but this dish couldn’t be more special, which is why it’s perfect for Christmas dinner.
I hope you all get to try it, you will be thanking me! And I hope you have a blessed, healthy, and joyfilled Christmas!
xoxo Katie
- 2 tablespoons unsalted butter, plus more for pan
- 2 1/2 pounds Russet or yukon gold potatoes, unpeeled, scrubbed, thinly sliced ( I used 1/8 inch on mandoline)
- 1 thick or 2 slimmer leeks, halved, washed, cut into 1-inch segments
- 2 cups heavy cream
- Kosher salt and freshly ground black pepper
- 2 garlic cloves, minced
- Leaves from 3 sprigs fresh thyme
- 1/2 cup plain breadcrumbs (panko or homemade are great here)
- 3/4 cup coarsely grated gruyère, comte, or baby swiss cheese
Heat oven to 350 degrees F. Generously butter an 8×12-inch or 3-quart baking dish. Cut garlic clove in have and rub all over the dish.Working in layers, arrange a layer of sliced potatoes on an angle, slightly fanned, in different directions filling the pan loosely. Sprinkle 1/3 of the leeks on top, then add another layer of sliced potatoes, repeating until you have 3 layers. In a medium saucepan, bring cream, 2 teaspoons kosher salt, 1/2 tsp. fresh ground black pepper, garlic, and thyme to a simmer, stirring to ensure the salt dissolves. Pour hot cream mixture evenly over the pan, trying to evenly coat the potatoes and leeks. Cover pan tightly with foil, place on a baking sheet to catch any drips, and bake for 30 minutes.
Meanwhile, melt 2 remaining tablespoons butter. Add breadcrumbs, salt, and pepper to taste and mix to evenly coat.
At 30 minutes, briefly remove pan from oven and remove foil. Sprinkle top evenly with cheese, then scatter with buttered breadcrumbs. Return to the oven without foil for 45 minutes, until potatoes are totally tender, the top is browned, and the edges are bubbly. [Insert a knife or skewer into potatoes to feel for crunch or resistance. Return to the oven if needed.]
Let cool for 10 minutes before serving hot.
Do ahead: Gratin can be assembled the day before and baked before a big meal. It can also be baked for 30 minutes (the foil-on portion) and cooled, finishing the baking time the next day. Gratin reheats well in a 350-degree oven. Leftovers keep in the fridge for 4 to 5 days.
