Make the dough: Stir together the flour, baking powder, and salt in a medium bowl and make a well in the center. Add the sour cream to the well and crack the eggs on top. Using your hand like a claw, stir the sour cream and eggs together, then gradually pull the dry ingredients into the center until you have a nice dough. Scrape out onto a lightly floured counter and knead a few times until everything is homogeneous. Cover the dough so it doesn’t dry out (I use an inverted bowl) and let it rest for 10 minutes.

When you return to the dough, you’ll notice how remarkably smooth and stretchy it has become! Give it a few more kneads, then let rest, covered, for 10 more minutes. Knead again, cover, and rest the dough for 30 minutes. Then refrigerate the dough, covered, until ready to use, or wrap tightly and freeze. (The dough can be frozen for up to 1 month. Thaw overnight in the refrigerator.)

Make the filling: Put the potatoes in a medium saucepan and add water to cover by a few inches (about 8 centimeters). Generously salt the water, bring to a boil over high heat, and cook until the potatoes are tender, about 10 minutes. Drain the potatoes and mash with a potato masher. Set aside.

In a medium frying pan, heat the olive oil and butter over low heat. When the butter has melted and stopped foaming, add the onion, spices, and a few fat pinches of salt and cook, stirring occasionally, until the onion is soft and starting to caramelize, about 20 minutes. Add the garlic and cook for another couple of minutes, until you can no longer taste raw garlic. Remove from the heat and stir in the sauerkraut, then turn the mixture out onto a cutting board and chop pretty small (but don’t lose your mind here). Transfer to a bowl, stir in the mashed potatoes and farmer’s cheese, and season to taste with salt and pepper. Let cool completely.

Once the filling is cool, use two teaspoons to form the mixture into 30 quenelles (i.e., resembling small footballs) and set on a sheet pan lined with parchment.

To assemble the pierogi: Put a clean, dry tea towel on a sheet pan and lightly dust it with flour. On a lightly floured work surface, with a lightly floured rolling pin, roll the dough out very evenly to about ⅛ inch. Cover the dough with plastic wrap and let rest for 10 minutes.

Using a 4-­inch (10-­centimeter) round cutter, stamp out as many rounds as you can from the dough, leaving them in place. Pull away the scraps, gather into a ball, and knead a few times; set aside.

Place one quenelle of filling in the center of each dough circle. Using a bench scraper to aid you (the dough is sticky and delicate!), lift one edge of a round of dough up and over the filling, aligning the edges. Press the dough to seal, then use the bench scraper to lift the dumpling from the table, starting from the folded side; recheck the seal and set the dumpling seam side up on the flour-­dusted tea towel. Repeat with the remaining circles of dough. Reroll the scraps of dough and stamp out more dough circles (you should have 30 in total) and repeat the filling and shaping; the rerolled dough will need to rest an additional 5 to 10 minutes to relax the gluten. Lightly cover the pan of assembled pierogi with plastic wrap and chill for at least 30 minutes, or up to 2 hours.

Bring a large pot of salted water to a boil. Fill a large bowl with ice and water. Remove the pierogi from the refrigerator. Using your index finger and thumb, pinch the edges of each one very well, thinning out the dough while creating a pretty ruffled edge and sealing in the filling forever; return to the tea towel.

Drop half of the pierogi into the boiling water. When they float to the surface, cook for 1 minute longer, then remove with a spider or slotted spoon and plunge into the ice bath. Once they are cool, remove from the ice bath and dry on a clean tea towel. Repeat with the remaining pierogi. (The boiled pierogi can be refrigerated in an airtight container for up to 2 days. Or you can freeze the boiled pierogi: Arrange them on a parchment-­lined sheet pan in a single layer and freeze until solid, then transfer to an airtight container and freeze for up to 2 months. Defrost in the refrigerator overnight before panfrying.)

When you are ready to serve, combine the butter and oil in a large frying pan and heat over medium heat. When the butter stops foaming, add half of the pierogi and panfry, turning as needed, until golden brown and puffy all over, especially on that ruffle! Transfer to a serving platter and repeat with the remaining pierogi. Sprinkle with the poppy seeds and serve immediately, with sour cream and Damson plum or sour cherry preserves alongside.

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