- 1 pound Celeriac, peeled, cut into 1/2-inch pieces (about 4 cups)
- 2 1/2 pounds Potatoes OR Turnips, cut into 1-inch pieces (about 61/2 cups)
- 1/4 cup (1/2 stick) unsalted butter, cut into pieces - 1/2 cup (or more) whole milk or ½ and 1/2
Cook celeriac in large pot of boiling salted water 5 minutes. Add potatoes/turnips to pot; cook until all vegetables are tender, about 20 minutes. Drain. Return vegetables to pot; stir over medium-high heat until dry, 1 to 2 minutes. Remove from heat; add butter. Using potato masher or immersion blender, mash vegetables until butter is incorporated. Add 1/2 cup milk; mash until almost smooth, adding more milk as needed. Season with salt and pepper.