Sour Cream & Onion Potato Pull-Apart Rolls

Yield: 18 rolls

1     medium (7 ounces) Yukon gold potato
½    cup reserved potato cooking liquid
2     teaspoons active dry yeast
1     bunch (about 6) scallions (2¾ ounces),
       cut into 1-inch pieces
4¼  cups bread flour, plus more for dusting
2     tablespoons, plus 2 teaspoons
       granulated sugar
2¾  teaspoons kosher salt
½    teaspoon freshly ground black pepper
⅔    cup sour cream
1     large egg
1     large egg yolk
8     tablespoons (1 stick) unsalted butter,
       cut into pieces, room temperature,
       divided
       flake sea salt, for sprinkling

Nutritional information per serving:
Calories 195 (34% from fat) • carb. 27g • pro. 5g • fat 7g • sat. fat 5g • chol. 34mg • sod. 349mg • calc. 12mg • fiber 0g

1. Place potato in a medium saucepan and add enough cold water to cover. Bring to a boil over medium-high heat, reduce to a simmer, and cook until tender, 35 to 40 minutes. Transfer potato to plate and let cool slightly. Reserve ½ cup of the cooking liquid on a liquid measuring cup; let stand until temperature is 105˚F to 110˚F. When liquid is cool enough, add the yeast and let stand until foamy, about 5 to 10 minutes.
2. Meanwhile, insert the medium shredding disc into the food processor. Peel the potato and shred.
Transfer to plate and reserve.
3. Replace the shredding disc with the chopping blade. Add the scallions and pulse to finely chop.
Add the flour, the 2 tablespoons of sugar, salt and pepper, and pulse to blend. Add the reserved potato, sour cream, egg, egg yolk, and 4 tablespoons butter to the work bowl. With the machinerunning on Low, slowly add the yeast mixture through the feed tube. Continue to process for 40 seconds to knead. The dough should be soft and slightly sticky.
4. Scrape the dough out onto a lightly floured surface and knead for 1 to 2 minutes, until smooth.
Refrain from adding flour. Use a bench scraper to unstick dough from surface. Shape into a ball and place in a greased bowl. Cover the bowl with plastic wrap and let rise in a warm place until 1½ times its original size, about 45 to 60 minutes.
5. Grease the bottom and sides of a 13 x 9-inch pan with 1 tablespoon butter. Divide the dough into 18 equal pieces (about 2 ounces each). Shape rolls, gently cupping your hand around the dough and using the work surface to roll it in a circular motion to form a tight ball. Arrange rolls in the prepared pan, spacing to make a 6 x 3 grid. Cover with plastic wrap and let rise in a warm place until nearly doubled in size, about 45 to 60 minutes.
6. Preheat the oven to 375°F. Melt 2 tablespoons of butter in a small saucepan. Evenly brush the tops of the rolls with butter and sprinkle with flake sea salt. Bake rolls until golden brown, about 18 to 22 minutes.
7. Meanwhile, melt remaining tablespoon butter. Remove pan from oven and immediately brush rolls with melted butter. Let cool in pan for 5 minutes, then carefully lift out and transfer to wire cooling rack.
8. Serve warm or let cool. Rolls can be baked 2 days ahead. Let cool completely and store airtight for up to 5 days at room temperature.