Recipe by Alexa Weibel
Start to Finish: 1 hour
3 1/2 lb. russet potatoes, peeled and chopped into 1-inch pieces
1 1/2 lb. parsnips, peeled and sliced into 1/2-inch pieces
1 1/2 sticks butter
4 large fresh bay leaves
3/4 cup heavy cream
8 oz. crème fraîche
3 large cloves garlic, grated
3/4 tsp. onion powder
1/4 tsp. freshly grated nutmeg
5 large egg yolks
1/2 cup olive oil
20 fresh sage leaves
Flaky sea salt, for sprinkling
1. Preheat the oven to 425°. In a large pot, cover the potatoes and parsnips with cold water. Bring to a boil over high heat. Generously salt the water. Reduce heat to medium. Cook the potatoes and parsnips until tender when pierced with a fork, about 15 minutes, then drain.
2. In the same pot, melt the butter with the bay leaves over medium-high heat until the butter is fragrant and golden, 5 to 8 minutes. Discard the bay leaves. Add the potatoes, parsnips, cream, crème fraîche, garlic, onion powder, and nutmeg. Using a potato masher, mash until very smooth. Stir in the egg yolks, 1 at a time, mixing well between additions. Season the mashed vegetables generously with salt and pepper.
3. Spoon the mashed vegetables into a large 3-qt. glass baking dish. Using the back of a spoon, create swirls or peaks on top.
4. Transfer to the oven. Bake, rotating the dish halfway through, until the parsnip potato mash is heated through and golden in spots, about 30 minutes.
5. Meanwhile, in a small saucepan, heat the oil over medium-high. Working in 2 or 3 batches, fry the sage leaves until crisp, 20 to 30 seconds per batch. Using a slotted spoon, transfer the sage leaves to a paper towel–lined plate; reserve the sage oil. Sprinkle with flaky sea salt. Just before serving, drizzle the baked parsnip-potato mash with the sage oil and top with the fried sage leaves.