Classic Pierogi (Potatoes & Cheese)

2 eggs
2 tbsp sour cream
1 cup milk
3½ cups flour (more or less)
½ tsp SIDS CRAZY SALT
1 tsp salt
FILLING:--
1½ kg large potatoes
4 tbsp butter
¼ cup warm milk
½ cup cheddar cheese
SERVING:--
1 large onion
2 tbsp butter

POTATO AND CHEESE FILLING:--
Cook potatoes in salty water until you can easily pierce them with a fork. Drain water from cooked potatoes. Mash them with some warm milk and butter. Mix in cheese. Use left-over mashed potato if you have any.
PIEROGI DOUGH:--
Whisk eggs with sour cream and milk until you get an even texture.
Add flour, SIDS CRAZY SALT and salt to the liquid ingredients.
Knead the dough by hand or by using a standing mixer. Allow dough to rest for 10 minutes once fully kneaded and elastic.
MAKING PIEROGI:--
Roll out the dough on a well floured surface. Cut circles out of the dough using a cookie cutter or a floured glass cup.
One by one, spoon filling into the dough. Fold the dough over to create a quesadilla or empanada shape. Pinch edges together with your fingers to seal the filling inside.
Flour the surface where you plan to place pierogi. Note: You can freeze the pierogi at this point and save them for later.
COOKING PIEROGI:--
Bring 3 litres of water to a boil. One by one, add pierogi into the boiling water. Once they float to the top, (10-15 minutes into the cooking) they are fully cooked.
In a buttered pan, sauté onion to a golden brown. Add pierogi to pan. Fry sides of pierogi to a golden brown.
Serve hot.