The classic gratin includes celery root, which is how it is often served in France. The celery root gives it a little more flavor to stand up to the strong flavor of the Gruyere. I used the Emmi Kaltbach Cave-Aged Gruyere, which has amazing flavor. I serve this as a side with duck breast and beef.
4 medium-size Yukon Gold potatoes (about 1.5 pounds) peeled and sliced thin
2 celeriac (celery root) about 1.5 pounds, sliced thin like the potato
2 cups whole milk
2 cups water (plus a little more to cover potato in pot if needed)
4 cloves of garlic minced
4 bay leaves
¼ t of sea salt
Fresh thyme – buy a bunch, trim about 3T of leaves to top the gratin, put the rest in the pot to boil potato
Freshly grated nutmeg
Freshly grated black pepper
1-cup heavy cream
½ Pound Gruyere cheese grated
Preheat the oven to 375 degrees and place a 2 qt gratin dish on the counter.
Slice the potato and celery root thin. Most important to try and keep the slices even thickness. I use my food processor with a slicing blade often or sometimes use a mandolin. Place potato and celery root slices in a pot and cover with milk and cold water. Add garlic, salt, bay leaves, and a bunch of thyme. You can tie the thyme together to make it easier to remove, or you can fish the pieces out after. Set your burner to medium-high and bring the liquid in the pot to a simmer, stirring occasionally so that the vegetables don’t stick to the bottom. Once simmering, turn the pot to medium heat, and cook for 10 minutes. You want to test the potato and make sure they are soft, but not falling apart.
When vegetables are cooked, drain in a colander to stop the cooking process. Arrange the vegetables in two layers in the 2 qt gratin dish. Sprinkle the first layer with Gruyere, black pepper, and nutmeg, and a half-cup of the cream. Repeat for the second layer topping it all off with the thyme leaves.
Cook gratin in the oven at 375 for 1 – 1.5 hours or until the top is golden brown. Remove from the oven, and allow cooling slightly before cutting into squares and serving.