These biscuits put leftover mashed potatoes and celeriac back to work, but there's no need to wait for leftovers for this recipe. It's just as good made with fresh mash as it is with day-old. If you don't have any celeriac on hand, use additional potatoes instead.
Be sure that your mash is very cold before adding it to the dough. A warm mash will melt the butter and leave your biscuits rubbery.
For the Mashed Potatoes and Celeriac
- 1½ cups peeled, chopped waxy potatoes
- 1 cup peeled, chopped celeriac (or additional potatoes)
- 1 cup heavy cream
- ¼ cup water
- ¾ tsp salt
- 2 tbsp butter
- 4 to 5 (6-inch) thyme sprigs
- Note: you can also use 1 cup leftover mashed potatoes plus ½ cup leftover mashed celeriac for this recipe. Be sure that they're both chilled.
For the Biscuits
- 2¼ cups all-purpose flour, plus more for dusting
- 1 tbsp plus 1 tsp cream of tartar
- 1 tsp baking soda
- 1 tsp salt
- ½ tsp black pepper
- 6 tbsp butter, chilled and cut into 1/2-inch cubes
- 1 cup plus 2 tbsp heavy cream, chilled (divided)
- ½ tsp flaky sea salt, for finishing
Preparation
- Make the potato–celeriac mash (if using leftover mash, skip this step): Stir together potatoes, celeriac, cream, water, and salt in a deep-sided saucepan. Add butter and thyme sprigs. Bring to a boil over medium-high. Reduce heat to medium to maintain a vigorous simmer, and cook, uncovered, stirring often, until the roots are very soft, about 20 minutes. Remove from the heat and discard the thyme. Transfer to a bowl and mash until totally smooth. Transfer to the refrigerator and chill until completely cold, at least 4 hours.
- Preheat oven to 425°F. Whisk together flour, cream of tartar, baking soda, salt, and pepper in a large shallow bowl. Add the butter and toss to coat with the flour mixture. Use a pastry cutter to blend the butter unto the flour mixture until it resembles tiny peas.
- Add 1½ cups of the fresh or leftover root mashes along with 1 cup cream. Using a sturdy rubber spatula, stir the mixture until a shaggy dough forms, adding the remaining 2 tbsp cream, 1 tbsp at a time, if needed. Chill, uncovered, for 20 minutes.
- Turn the dough out onto a floured work surface. Sprinkle the dough with flour and pat or gently roll into a square. Using a floured knife, cut the dough into quarters. Stack the quarters on top of each other and press down into another square shape. Repeat this process 3 times, adding additional flour to the work surface as needed.
- Trim the edges of your final dough square into neat lines. Cut the dough into 16 or so squares. Line a baking sheet with parchment paper and arrange the squares ¾-inches apart.
- Sprinkle the biscuits with flaky salt, if desired. Transfer to the oven and bake until golden brown, 20-25 minutes. Allow to cool on a wire rack for at least 5 minutes before serving.
