In a bowl, whisk together the flour with the salt.
Add the egg and combine. The dough should be clumpy.
Gently work in the sour cream and room temp butter until the dough comes together. As it starts to combine and work together, gently knead and fold the dough with your fingers until it becomes less sticky and is still moist.
Wrap the dough in plastic wrap and refrigerate for at least 30 minutes and up to 48 hours.
While the dough sits: Peel the potatoes, cut them into cubes and boil them to make mashed potatoes. Once boiled. Mash the potatoes then add in the cheddar cheese until it is melted and combined with the potatoes. Let the potato mixture cool.
Once the dough is chilled, split the dough in half so it is easier to work with. Roll it out until it is 1/8in thick. Cut out 2-2.5 inch circles of dough. You can reroll out the scraps of dough. Repeat this with the other half of the dough.
Place about 1-1 1/2 tsp of filling on each round of dough, depending on the size of each round. Fold the dough over the filling and pinch the edges of together to seal it shut. Then, seal it again with the tines of a fork.
Boil a large pot of water. Once boiling, add 1-2 pierogi to the water to get a feel for how to cook these. They will sink at first, but once they float to the top, remove them from the water and place in a lightly sprayed air fryer basket.
Once you get the hang of it, you can boil multiple pierogis at once. The amount you can put in the pot depends on the size of the pot you are using. Don't overcrowd because they need room to float without sticking together. I did about 4-5 at a time.
Once the air fryer basket is filled with pierogis, without having them touch or overlap each other. Gently spray them with oil. Cook for 8 minutes at 400 °F and filling each pierogi at the halfway point. Continue cooking until they are golden brown to your liking.
Remove pierogis and repeat with remain pierogis.
Remove from the air fryer basket and enjoy with condiments such as sour cream, apple sauce, or whatever your favorites are!
Notes
Replace the potato filling with your own personal favorite filling!