To make the dough: 

In the bowl of a stand mixer fitted with a dough hook, mix together the flour and salt. Add the egg, then slowly drizzle in the water. Mix until a dough forms, then knead until the dough comes together into a smooth, elastic ball, 10 minutes. If you don’t have a mixer, you can do this by hand, but knead for 20 minutes. (And be prepared to sweat!)

Wrap the dough in plastic wrap or place in a covered container, and let rest at room temperature for at least 1 hour before using.

To make the dough: 

In the bowl of a stand mixer fitted with a dough hook, mix together the flour and salt. Add the egg, then slowly drizzle in the water. Mix until a dough forms, then knead until the dough comes together into a smooth, elastic ball, 10 minutes. If you don’t have a mixer, you can do this by hand, but knead for 20 minutes. (And be prepared to sweat!)

Wrap the dough in plastic wrap or place in a covered container, and let rest at room temperature for at least 1 hour before using.

To make the filling: 

In the bowl of a stand mixer fitted with the paddle attachment, combine the beef, pork, veal, onion, ice water, and kosher salt. Mix until the mixture comes together, 1-2 minutes. You’re looking for the fat to emulsify, which will incorporate all of the ice water and onion liquid and coat everything with a nice, fat-smeared sheen. If you stop the mixer and grab a pinch of the mixture, it should stick to your fingers with a very tacky feel. Under- or over-processing will lead to dry meat, so try to hit this nice sticky sweet spot — stop between pulses and check the texture.

Refrigerate until ready to assemble the pelmeni. This filling is best made the same day you are assembling, but can be made up to a day ahead if needed.

To make the dough: 

In the bowl of a stand mixer fitted with a dough hook, mix together the flour and salt. Add the egg, then slowly drizzle in the water. Mix until a dough forms, then knead until the dough comes together into a smooth, elastic ball, 10 minutes. If you don’t have a mixer, you can do this by hand, but knead for 20 minutes. (And be prepared to sweat!)

Wrap the dough in plastic wrap or place in a covered container, and let rest at room temperature for at least 1 hour before using.

To make the filling: 

In the bowl of a stand mixer fitted with the paddle attachment, combine the beef, pork, veal, onion, ice water, and kosher salt. Mix until the mixture comes together, 1-2 minutes. You’re looking for the fat to emulsify, which will incorporate all of the ice water and onion liquid and coat everything with a nice, fat-smeared sheen. If you stop the mixer and grab a pinch of the mixture, it should stick to your fingers with a very tacky feel. Under- or over-processing will lead to dry meat, so try to hit this nice sticky sweet spot — stop between pulses and check the texture.

Refrigerate until ready to assemble the pelmeni. This filling is best made the same day you are assembling, but can be made up to a day ahead if needed.

To assemble and cook the pelmeni: 

Divide the dumpling dough into 8 equal balls, and grab a spray bottle of water (or, if you don’t have one, a dish of water and a pastry brush), a straight-sided rolling pin, and a rimmed baking sheet dusted with flour.

Liberally dust the top of your pelmenitsa with flour. Take 1 ball (leaving the rest covered with a dish towel so they don’t dry out) and roll it out on a lightly floured countertop until it’s slightly larger than your mold. Drape the rolled-out dough over your pelmenitsa so that it reaches over the ends of the mold. Press or pat the dough lightly so that an imprint of the mold below is made on the dough.

Using 2 spoons or a pastry bag fitted with a wide tip, scoop or pipe a small blob of filling into each of the 37 divots. You’ll need just a heaping teaspoon or so in order to still be able to seal things (don’t get carried away!).

When you have piped filling into all the slots, roll out a second piece of dough until it’s slightly larger than your mold. Lightly spray some water over the top of your filled pelmeni (lightly brush the exposed dough with water if you don’t have a spray bottle), then gently place the second round of dough over the top.

Firmly roll over the top with your rolling pin several times to seal the pelmeni and cut the dough between them. Turn the pelmenitsa upside-down over the prepared baking sheet, and nudge the filled dumplings out, separating them with your fingers if needed.

Repeat with the remaining dough and filling. At this point, the dumplings can be cooked (instructions below) or frozen for future use (freeze directly on the baking sheet, then transfer to a sealed plastic bag).

Bring a large pot of salted water to a boil. Add the dumplings (use about 20 per person). Adjust the heat as needed to maintain a healthy-but-not-too-vigorous boil. Give the dumplings a few good stirs, making sure to get your spoon all the way to the bottom of the pot to free any dumplings that may have stuck to the bottom.

Cook until the dumplings rise to the surface, and then for 1 minute more — this will take 4-5 minutes total. Additional time may be needed depending on the heat of your burner and whether or not the dumplings are frozen. If you’re not certain whether they’re done, remove 1 dumpling and cut it in half — the meat filling should be cooked through.

In a large bowl, combine the softened butter, vinegar, and salt to taste.

Once the dumplings are cooked, skim them out of the boiling water with a slotted spoon or drain in a colander, shaking off the residual water. Place them in the prepared bowl and toss — the softened butter and vinegar will come together with the heat of the dumplings and the motion of stirring, emulsifying into a sauce. Keep whirling them around in the bowl until all of the butter is incorporated.

Transfer the dressed dumplings to a serving dish and top with a generous dollop of Smetana, crème fraîche, or European-style sour cream, then the fresh herbs.