Mix together the flour and the salt in a large bowl. Add the water slowly, mixing the flour and water until it comes together into a dough.
Knead the dough on a floured work surface for 3-4 minutes until it is smooth. It will get dryer as you knead it, so you can add a splash more water if it feels dry. If it still feels wet and sticky after kneading, add a little bit of flour.
Add the potatoes to a microwave safe bowl with a splash of water in the bottom. Cover them, allowing a small escape for steam. Microwave on high for 4 minutes until soft. Mash until smooth and season with salt and pepper to taste*.
To make the tofu cottage cheese, squeeze a bit of water out of the tofu with your hands. Add it to a large bowl, and mash it up roughly with a fork.
To the tofu, add the yoghurt, nutritional yeast, apple cider vinegar and salt. Mix well until it resembles the texture of cottage cheese.
To make the mushrooms, heat the oil in a large frying pan. Add the mushrooms, and fry over a medium-high heat for 2 minutes until slightly wet.
Add in the smoked paprika and salt, and fry for 3-4 minutes until dry, stirring and scraping up the spices from the bottom as you go.
Mix together the mashed potatoes, mushrooms and tofu cottage cheese. Check for seasoning and add salt and pepper to taste.
Split the dough into two pieces. On a lightly floured surface, roll out one piece to ~2mm thick. Use a circular cookie cutter or a glass to cut out 8-9cm circles.
Roll small balls out of the filling and place one in the middle of each circle.
Pick up a circle of dough and fold it in half over the ball of filling. Press down around the edges to seal it in a half moon shape. If the dough is too dry and not sticking together, you can use your finger to dab a little water along the seal.
Use a fork to fully seal the pierogi around the edges. Repeat for each circle.
Bring a large pot of salted water to the boil. Add the pierogi in batches, making sure not to overcrowd the pan. Bring the water to a simmer, and once the pierogis have come to the surface, cook for 3 more minutes before removing them with a slotted spoon.