Prepare pierogi dough of choice and let rest for 30 minutes.
Wash the asparagus and remove the woody ends of each spear. Cut them in half and cook them in salted water for 7-8 minutes until soft.
Drain the water and cook the spears on low heat for another 3 to 4 minutes to evaporate remaining water.
Cut the asparagus into thin slices and transfer into a large bowl and combine with mascarpone cheese, salt, and pepper. Stir well and taste to ensure it's seasoned to your liking.
Divide dough into 2-3 parts. Roll one part thin on a floured surface, but not so thin that it tears. Wrap remaining dough to prevent drying.
Cut palm-sized circles in the rolled dough. Reuse the leftover dough by forming a ball and rolling again.
Place a spoonful of asparagus filling on each dough circle, fold over, and seal edges, removing as much air as possible. Moisten edges for a better seal. Place formed pierogi on a floured sheet, covered with a damp kitchen towel. Use flour to prevent sticking if they touch. Repeat until all dough or filling is used.
Boil a large pot of salted water (1 tsp salt per quart).
Add pierogi to boiling water, stirring to prevent sticking. Simmer gently for 3-4 minutes after they float to the surface.
Remove with a slotted spoon and serve.