Feta-Spinach Potato Pierogi, Garlic Onion Butter

Steps

1. Make the dough first: in a bowl, mix the flour with one third of the salt. Add the sour cream, egg and warm water and stir into a shaggy dough. Knead 5 minutes until smooth, cover and rest 30 minutes.
2. While the dough rests, put the potatoes in a pot, cover with cold water (extra tap water, not the measured water) and boil 15 minutes until very tender. Drain well and mash.
3. Melt one fifth of the butter in a large skillet over medium heat and cook the spinach 2 minutes until wilted. Stir the spinach into the potatoes with the feta, dill, black pepper and another third of the salt. Let the filling cool.
4. Roll the dough on a floured surface to about 1/8 inch thick and cut 24 rounds about 3 inches wide, rerolling scraps once.
5. Place a spoonful of filling on each round, fold into a half-moon and pinch the edges firmly to seal.
6. Bring a large pot of water to a boil. Cook the pierogi in batches for 3 to 4 minutes after they float, then lift out with a slotted spoon. The egg dough is fully cooked once tender and floating, well past 160°F (71°C).
7. Wipe the skillet and melt half of the remaining butter over medium heat. Add the onion and the last third of the salt and cook 15 minutes, stirring, until deep golden. Stir in the garlic for 1 minute, then move the onion butter to a bowl.
8. Melt the rest of the butter in the skillet and fry the boiled pierogi 2 minutes per side until crisp and golden.
9. Serve the pierogi topped with the garlic onion butter.