serves 4 to 6 as a side dish
Celeriac and potatoes are a natural match. They are combined at proportions of two to one in this recipe, but use equal amounts for an even more pronounced celery flavor. For a hearty meal, serve this mash with some greens (in a salad or cooked) and a few fat sausages.
1 large celery root
4 medium-size potatoes
5 tablespoons butter
1 medium-sized onion, peeled and finely chopped
1 1/4 cup heavy (whipping) cream
1 large bay leaf preferably fresh
1 teaspoon fresh thyme leaves or 1/2 teaspoon dried
salt and freshly ground black pepper
1 tablespoon chopped fresh flat-leaf parsley leaves
1. Fill a medium-large saucepan halfway with water, and bring to a boil over high heat.
2. While water is heating, trim and peel celeriac, removing all brown parts and cutting off whatever remains of the leafy top. Scrub it clean, and then cut it into 1-inch chunks.
3. Scrub the potatoes but do not peel them. (The puree would be more elegant, but less nutritious, without the potato skins.) Cut them into 1-inch chunks.
4. Add the celery root and potatoes to the boiling water and return it to a boil. Then reduce the heat to a brisk simmer and cook, partially covered, until both vegetables feel soft when pricked with a fork, 15 to 20 minutes. Drain and set aside.
5. Rinse and dry the pan, and then put it back over low heat. Add 2 tablespoons of the butter, and when it has melted, add the chopped onion. Cook, stirring, until the onion is soft and translucent, about 10 minutes.
6. Add the cream, bay leaf, and thyme. Simmer very slowly so the herbs will steep in the cream and flavor it, about 5 minutes. Then remove and discard the bay leaf.
7. Add the potatoes and celeriac to the cream mixture and stir for several minutes to combine and reheat. Mash with a hand potato masher or an immersion blender right in the pan. (Resist the urge to use a ricer, which works for potatoes but turns celery root into a grainy mess.) Add salt to taste, and then set the pan aside, covered.
8. Place the remaining 3 tablespoons butter in a small non-aluminum pant that does not have a dark bottom (so you can track the changes in color), and melt it over medium-low heat. It will bubble and foam, so watch it and turn the heat down if it seems about to boil over. The milky particles will darken and sink to the bottom, but should not blacken. The butter will turn a slightly brown color, with a wonderful rich flavor.
9. Spoon the mashed mixture into a warmed shallow bowl, making a shallow pattern of swirls or ridges on top. Pour the brown butter over the top, so that it collects in the hollows. Grind black pepper to taste over the top, sprinkle with the parsley, and serve hot.