For farmers cheese filling: Combine together sugar with farmers cheese, until sugar is well mixed in. Set a side. If you are making filling with blueberries and sugar, combine they together right before you make vareniki.
For a blueberry filling: rinse under cold water blueberries, dry with a paper towel. Sprinkle with sugar and set a side.
Whisk eggs with sour cream, until it has one texture. Add flour 1 cup of flour, salt and sugar. Mix with a stand up mixer or spatula in until all ingredients are well combined. Add water and milk, mix until you will receive one texture. Slowly add the rest of the flour(3 cups).
Place mixture on floured surface. Knead the dough with kitchen aid mixer or your hands. Dough should turn out soft but at the same time should not be sticky. Don't use too much flour otherwise dough will come out very rough.
Roll out the dough on well floured surface. Using cup cut out circles out of dough, you can flour cup so it would be easier to cut out circles.
One by one fill your circles with filling (place in middle of circle), turn over edge and tight up edges together with your fingers, make your its tight enough for your feeling not to fall out.
Flour surface where you will place vereniki, you can place them in cooking sheet and freeze them, after frozen can store in ziplock bag.
Bring pot of water up to boil. Add vareniki, cook until they float up to the top.
Drain and top with melted unsalted butter. We also add sometimes sour cream, jam and sugar.