Make the apple butter: peel and core apples. Cut apples into eight pieces each. Put into small sauce pot with 1 cup of water. Cook on medium heat until apples are soft and mushy. Blend until smooth. Return apple sauce to sauce pot and cook on very low heat until apples are a dark brown, stirring constantly.
Make the filling: boil potatoes until fully cooked. While potatoes are cooking, render bacon until crispy. Once crispy, discard ½ of the rendered bacon fat. Add sliced scallion and cook for 30 seconds. Combine, bacon, scallions, sauerkraut, cooked potato, sour cream, and 1 tsp. of salt. Mix and mash until potatoes are smashed and creamy. Reserve filling.
Make the dough: combine butter, salt, and flour. Mix until butter is evenly distributed. Add boiling water and mix until dough is elastic. Let rest 15 minutes while wrapped in plastic wrap.
Make the pierogis: divide dough into 4 parts. Onto a lightly floured surface, roll out thinly the first piece of the dough, to a thickness of approx. 2 mm or 1/16 inch. If the dough is hard to roll out, set it aside for about 5-10 minutes to rest. Use the top of a cup or a pierogi/pastry cutter to cut out rounds. Place about 1 tsp. of filling on each round. Gather scraps, cover with plastic wrap and set aside. Fold the dough over the filling to create a half-moon shape. Press edges together, sealing and crimping with your fingers. Do not leave any gaps or pierogi may open during cooking. Place the pierogi aside on a towel lightly sprinkled with flour (this is important, they can stick to the board), cover loosely with a kitchen cloth so that they don‘t dry out. Repeat with the remaining dough.
Cook and serve: boil pierogis for 3-4 minutes, then brown one side in a sauté pan with butter on medium heat. Serve over apple butter and shave aged cheddar over the top. Serve immediately.