Step 1

Dough: In a mixing bowl, whisk together the sourdough starter, water and egg. Next add the salt and flour, and work the mixture into a dough with your hands or a spatula. Depending on the hydration of your starter, you may need to add extra flour or water to get the dough to come together. If it feels pretty tacky after adding the initial flour amount, you can add a couple tablespoons at a time while kneading until it firms up. If it feels too dry, sprinkle over a tablespoon of water at a time while kneading to get it right. Knead in the bowl until you have a smooth dough. Wrap in plastic and chill in the refrigerator for at least two hours, but overnight is fine too!

Step 2

Caramelize onions: In a large frying pan, melt a tablespoon or two of butter on medium heat. Add the sliced onions and sprinkle with salt and pepper to taste. Stirring occasionally, allow the onions to saute until they become fragrant and start to caramelize and turn golden.

Step 3

Filling: Cook your potatoes in salted water and drain when fork tender. Mash the potatoes until they are smooth. Add the cheese, sour cream, about 1/2 cup caramelized onions, salt and pepper and mix to combine. Taste and adjust the seasoning as necessary. Allow to cool to room temperature.

Step 4

Assembly: Divide the chilled dough into two, keep half in the fridge and roll out the other half on a well floured surface to about 1/8th inch thick. Using a biscuit cutter or a glass, cut into 2 inch rounds. Plop about a heaping teaspoon of filling into the middle of each, brush the edges with a little water, fold it in half and then crimp the edges with your fingers. Place on a flour dusted baking sheet (and cover with a towel as you work so they don't dry out). Repeat the rolling with the other half of dough, and continue until they are all filled. You can re-roll the scrap dough too (def recommend chilling again before rolling though). Chill the pierogi in the fridge or freezer while you bring your water to a boil.

Step 5

Cook 'em: Bring a large pot of salted water to a boil and place up to 6 pierogies in at a time (don't overcrowd the pot; boil in batches). When they rise to the top of the pot, drain them and serve with caramelized onions and sour cream. You can also at this stage after boiling, pan fry them in a little butter for a crispy exterior, and buttery sauce (which is my fave way to eat 'em!).