Mix the flour and salt in a large bowl. Stir in the melted butter, sour cream, and egg. Stir until somewhat combined, then knead with your hands for about 8 minutes until smooth. Wrap and set aside in the fridge at least a half hour.
Mix the potatoes, cheese, and corned beef in a bowl to combine.
Roll the dough thin, about 1/8th of an inch. Cut out rounds, I did 2.5 inches. Place about 1 and a half tablespoons of the filling onto the dough round, and use your finger to rub a small amount of water on the edge of the dough. Fold the dough over the filling forming a half moon shape. Use a fork to seal the dough around the edges.
Put the sauerkraut into a frying pan with some oil over medium high heat. Cook about 30 minutes, stirring often, until blackened in some areas and browned in others.
Mix the sour cream, hot sauce, and lime juice in a bowl. Season with salt.
Bring some water to a boil and boil the pierogi for about 3 minutes to cook. Remove from the pot and toss with some oil.
Bring a pan to high heat with a little oil. Add the pierogi, in batches if needed, and brown on both sides. Remove from heat.
Plate the pierogi and top with the sauerkraut, sour cream, and scallions.