Rinse the lentils under cold water.

In a pot, combine lentils with 2 cups of water and the bay leaf.

Bring to a boil, then reduce heat and simmer for 20-25 minutes until tender but not mushy.

Drain, discard the bay leaf, and let cool.

In a skillet, heat oil over medium heat.

Sauté the chopped onion until soft and golden, about 5 minutes.

Add the sauerkraut, dried thyme, smoked paprika, and marjoram. Cook for another 5-7 minutes until fragrant.

Stir in the cooked lentils, black pepper, and salt. Mix well and cook for 2-3 minutes, then remove from heat and let the mixture cool completely.

Transfer the filling into food processor and pulse a few times to create a smoother texture.

In a large bowl, combine the flour and salt.

Add the egg, sour cream, and oil, then gradually pour in warm water while mixing.

Knead the dough for about 8-10 minutes until smooth and elastic. Cover with a damp cloth and let rest for 30 minutes.

Roll out the dough on a floured surface to about ⅛ inch (3mm) thickness.

Cut out circles using a glass or cutter (about 3 inches/8cm in diameter).

Place about one tablespoon of filling in the center of each circle.

Fold the dough over the filling to create a half-moon shape, pressing the edges firmly to seal. Use a fork to crimp the edges for extra security.

Bring a large pot of salted water to a boil.

Drop the pierogi in batches and cook until they float to the surface, about 3-4 minutes.

Remove with a slotted spoon and drain.

Serve warm with sour cream and fresh dill or dill sauce.

For extra texture, pan-fry the boiled pierogi in butter until golden and crispy.

Garnish with crispy fried onions if desired.