Use a 1 teaspoon measuring spoon to scoop portions of the chilled dal filling and roll them into balls in the palms of your hands. Refrigerate the filling until ready to form pierogi.
Divide your pierogi dough in half and cover whichever half you aren’t using. On a lightly floured surface, roll and stretch your dough to about ⅛″ thickness. Use a 2½″ (2.5″) circular cutter to cut as many rounds of dough out as you can. Save any scraps to re-roll later.
Lightly dust a sheet pan with with flour or corn starch. You’ll put your shaped pierogi here once they’re done. The flour helps keep them from sticking to the pan and to each other.
Take one circle of dough and hold it in the palm of your non-dominant hand. Place a ball of dal filling in the center, and cup your hand to fold the dough in half around it. Use your dominant hand to pinch the dough together at the top. You may need to stretch the dough just slightly to get it to meet at the top, but it should be soft enough that it stretches easily. Continue pinching firmly down each side of the pierogi around the filling to seal.
Turn the pierogi on its side and gently flatten between your palms to encourage the filling to spread into any gaps, and pinch the seams again to make sure they’re secure and there are no air pockets inside.
Repeat with the rest of the dough and rest of the filling, working in batches if you need to.
Place the finished pierogi in rows on the sheet pan. They can touch slightly, but if you’re planning on freezing them don’t let them overlap too much or they’ll stick to each other. If not cooking immediately, freeze on the sheet tray for 20-30 minutes before transferring to an airtight container and returning to the freezer.