Steps:

To make the dough, combine the flour and salt in a large bowl. Gradually add water, mixing until a dough forms. Knead on a floured surface until smooth. Cover and let rest for 30 minutes.
For the filling, boil the potatoes until tender. Drain and mash.
In a skillet, heat olive oil over medium heat. Add the onion and cook until soft and golden. Mix the onions with mashed potatoes, season with salt and pepper.
Divide the dough into small portions. Roll each into a circle, and place a spoonful of filling in the center. Fold over and seal the edges.
Bring a large pot of salted water to a boil. Cook the pierogi in batches until they float to the top, about 3-4 minutes. Drain.
Serve hot, garnished with fresh herbs if desired.

Vegan Pierogi with Potato and Onion Filling