To make pelmeni, divide the dough into 4 equal pieces. Take 1 piece of dough and cover the rest with plastic wrap, roll out the dough into a large circle 1/8 inch thick.
Using a 2 inch cutter or glass cup, cut dough into circles. Next, place about 1 teaspoon of filling in the middle of the circle, fold in half and seal the ends together using fingers, then bring two ends together and pinch and seal to make a dumpling. Place each dumpling onto a floured surface.
Repeat until all filling and dough is gone. When half way done, bring a large pot of water with 1 tablespoon of salt to a boil.
Place half of the pelmeni into the water and bring it to a boil, stirring few times. Once pemeni starts boiling reduce to medium heat and simmer for about 5 minutes or until the filling is cooked thru, stirring few times.
Finally, using a slotted spoon remove pelmeni onto a plate and immediately add butter, then stir. Serve with a sprinkle of black pepper, sour cream and a splash of white vinegar (vinegar is totally optional, it is my favorite tho with pelmeni). Enjoy!