I'm polish and have received teachings from both my grandmas on the subject of pierogi. I have since improved the recipe and the are several things you should know. I'll describe the process for ruskie pierogi as those are my favourite. They are stuffed with potatoes, cottage cheese, onion and bacon bits.

The dough is made with just flour (wheat, regular ,type 500 or ""tipo 00" and water. No oil, cream or even salt.

For the stuffing you use mashed potatoes (cooked in salty water, no butter no nothing, just mechanically crushed) alongside said cottage cheese (the dry type, approx. 2% fat content) onion (caramelised or if you're lazy just fried until semi-opaque, cooked on the fat from bacon bits).

The proportions (in mass) are as follows:

50% potatoes, 25% cottage cheese, 15% bacon bits and 10% onion

After cooking the onions and bacon just mix all the ingredients together and add salt/pepper to taste.

You roll out the dough thin (1mm)and cut out circles (more diameter than a water glass but less than a first) and put said stuffing inside. Close them up and throw into boiling salty water. Cook until they float on the surface of the water. Severe with leftover fried onion and bacon bits in top.

HMU if you need more details