How to Make It
In a bowl, mix together the flour, sour cream, egg olive oil, and salt until the ingredients bind together. Place the dough on a lightly floured surface and knead for a couple minutes, or until smooth. Wrap in plastic wrap and let rest for 30 minutes.
Heat a large skillet over medium-high heat. Add the oil, and then stir in the carrots. Cook the carrots for 10 minutes. Stir in the celery and continue cooking 5 minutes, or until vegetables are tender. Stir in the beef and cook for another 10 minutes or until beef is browned and cooked through and the vegetables are soft. Season with salt and pepper, remove from heat and set aside.
On a lightly floured surface, roll out the dough to about 1/8-inch thick. Using a 3-inch round cutter, cut out 12-15 rounds. Brush the edges of each round lightly with water, then place 1 tablespoon of filling on one side of the rounds. Fold the dough over, making half moon shapes, pressing out the air. Press and crimp the edges to seal the pierogi.
Bring a large pot of salted water to a rolling boil. Cook the pierogi for 3-5 minutes, or until tender. Drain.
Heat the butter in a large skillet over medium heat. Add the pierogi to the skillet with the butter and sear each side for about 1 minute or until golden. Serve warm with the sour cream.