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.
Place the potatoes and 1/2 teaspoon salt in a large pot and fill with cold water to cover the potatoes. Bring the water to a boil over high heat, then reduce heat to medium-low and then simmer for 10-15 minutes or until the potatoes are tender when pierced with a fork. Drain potatoes and mash. Allow to cool.
Heat a large skillet over medium heat. Crisp the bacon, then remove the bacon from the skillet, reserving the bacon grease in the skillet. Cut the bacon into 1/2-inch pieces. Reserve a handful of the bacon pieces, then combine the mashed potatoes and remaining bacon.
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 skillet with the bacon grease over medium heat. Add the pierogi to the skillet and sear each side for about 1 minute or until golden. Remove from the pan.
Add the remaining 4 tablespoons of butter to the skillet. Allow the butter to foam, then settle down. Add the thyme leaves and continue to cook until the butter just begins to brown and develop a toasty, nut aroma. Season with salt.
Spoon the thyme butter over the pierogi and serve warm garnished with the reserved bacon pieces.