Pierogi Two Ways: Lentil-Onion and Sweet Potato Cheddar

I had made pierogi once before from this cookbook (with kasha-mushroom filling - March), and had forgotten how divine the dough is.  Teeming with sour cream, butter and eggs, (and I snuck in a little whole-wheat flour!) it smelled heavenly while I prepared the dumplings. I rolled it out, cut it in circles with a cup, and filled the circles with (a) boiled green lentils, sauteed onions, salt and pepper or (b) mashed sweet potato, cheddar cheese, sauteed onions, salt and pepper.  The sweet potato filling was much easier to manage, in part because it wasn't as wet as the lentils, which made it hard to seal the dumplings.  After folding the circles in half and chilling them in the fridge for a while, I boiled the pierogi for five minutes and tossed them in butter.  Hearty, toothsome and satisfying - the definition of comfort food - this is a recipe I'd definitely make again.  Yum!