Boil the vareniki in salted water over moderate heat for 5-7 minutes, or until they float to the surface. Then, use a slotted spoon to transfer them to a colander. Once the water drains, place them in a pot, drizzle with melted butter, and give them a gentle shake. Berry-filled vareniki are taken out of the boiling water, cooled on a board, and served with sour cream, sugar, or syrup.
If you’re not cooking the vareniki right away, prepare the dough using a cold method. Mix the flour with cold water or milk. Dough made with cold water doesn’t dry out as quickly.
Stiff dough can be difficult to roll out and shape into vareniki, so it’s better to make it soft and then gradually add flour.
If you’re in a hurry and want to quickly shape the vareniki, roll out the dough into a large rectangle. Place the filling in even rows about 2 inches from the edge. Cover this with a second layer of rolled-out dough and cut out the vareniki using a cutter.
Roll out the dough scraps into a ball and place it in a plastic bag. In the morning, you can make dumplings and fill them with cheese or sour cream.