Sweet Potato Gnocchi with Sage Butter

Ingredients

• 3 pounds (1.4 kg) sweet potatoes (about 6 medium potatoes)
• 1 tablespoon (9 g) Diamond Crystal kosher salt; for table salt, use half as much by volume or same weight
• 3 ounces (85 g) Parmigiano-Reggiano, finely grated, plus more for serving
• 3 large egg yolks, lightly beaten
• 1 1/2 cups all-purpose flour (6 3/4 ounces; 191 g), plus more for dusting and shaping
• 8 tablespoons unsalted butter (4 ounces; 113 g), plus 1 tablespoon (1/2 ounce; 14 g) chilled unsalted butter for finishing
• Leaves from 1 large sprig fresh sage (about 15 large and small leaves)
• 1 tablespoon (15 ml) fresh lemon juice, optional (see notes)
• Lemon zest, for serving
• Aleppo pepper, for serving

Instructions

1. Adjust oven rack to middle position. Place 3 large sheets of heavy-duty aluminum foil on a work surface. Working with 1 sheet at a time, place about 2 potatoes in center. Fold up foil and crimp edges to tightly seal. Repeat with remaining potatoes and foil. Transfer pouches to a rimmed baking sheet and place in the oven. Set oven to 300°F (150°C). Roast until a thin skewer inserted into potatoes meets some resistance, 1 1/2 to 1 3/4 hours. Carefully unwrap and discard foil and place unwrapped potatoes in an even layer on the same baking sheet. Increase oven temperature to 400°F (205ºC), and roast until sweet potatoes are caramelized and a thin skewer inserted into potatoes meets no resistance, about 30 minutes (see notes). Remove potatoes from oven and set aside until cool enough to handle, 10 to 20 minutes. (Set baking sheet aside and do not turn off oven.)
2. Transfer sweet potatoes to a work surface or cutting board. Using tongs to hold hot potatoes, slice each in half lengthwise.
3. Using a spoon, scoop out sweet potato flesh, and transfer flesh to a large bowl. Add salt and mash with a potato masher or fork until mostly smooth. Line reserved baking sheet with aluminum foil. Transfer potato mixture to aluminum foil-lined baking sheet and spread it into an even layer. Return potatoes to oven and cook until they appear drier, about 15 minutes, stirring halfway through.
4. Press potato flesh onto a clean work surface, spreading it into an even layer, and allow steam to escape for a few minutes. Top evenly with Parmigiano-Reggiano and drizzle egg yolks all over potatoes.
5. Sift flour evenly on top of sweet potatoes. Using a bench scraper, chop down repeatedly all over to cut Parmigiano-Reggiano, egg, and flour into potatoes. Use a bench scraper to gather the shaggy sweet potato mixture into a loose mound. Pat it together, adding flour to the dough and work surface as necessary, until mixture holds together. Shape mixture into a roughly 15-inch log (log won't be perfectly smooth or firm).
6. Clean work area well and dust work surface and sweet potato log with fresh flour. Using bench scraper, slice off a roughly 1-inch-thick portion of dough and roll into a snake about 1/2-inch thick; use a light touch as you roll, trying to use your palms more than your fingers, and dusting as necessary with flour to prevent sticking. Repeat with remaining dough. Transfer snakes to a well-floured area or baking sheets as you go.
7. Using bench scraper, cut each snake into 1-inch portions, trimming off uneven ends as necessary. Transfer gnocchi to a well-floured baking sheet or other well-floured surface.
8. Bring a large pot of very well-salted water to a boil. Meanwhile, melt 8 tablespoons (4 ounces; 113 g) butter in a large stainless steel skillet over medium-high heat until it foams. Add sage and fry until very aromatic and milk solids in butter begin to brown, 1 to 3 minutes. Set aside off heat.
9. Using a bench scraper or slotted spatula to scoop them up, transfer gnocchi to boiling water. Once they're all transferred, gently stir once with a spider skimmer or slotted spoon to prevent sticking. Cook until all the gnocchi float to the surface, 2 to 3 minutes. Continue to cook until gnocchi is soft yet cooked through, without any raw flour flavor, about 1 minute.
10. Using spider or slotted spoon, scoop gnocchi directly into skillet with sage butter, allowing some of the water clinging to them to come along. Cook gnocchi in sage butter over medium-high heat, tossing very gently, until gnocchi are glossy and evenly coated with butter, about 1 minute. Off heat, finish gnocchi with lemon juice, if using, and 1 tablespoon chilled butter. Toss very gently until gnocchi is evenly coated in a creamy sauce.
11. Carefully spoon gnocchi into serving plates and top generously with finely grated Parmigiano-Reggiano, lemon zest, and aleppo pepper. Serve immediately.