Add flour to a mixer and make a well. Add the two eggs to the well with 1/2 cup of water. Mix all ingredients until the mixture is smooth. Add more water or flour so that the dough isn't too sticky or runny. Flour a large cutting board, pastry slab, or the counter, like I do. Roll the dough out to about 1/8 of an inch. Cut circle out with the top of a glass or ramekin. Fill the circle with 1 teaspoon of mashed potatoes, then fold the dough circle in half, sealing in the potatoes by running your finger with some water on it, around half the circle. Pinch closed. Set aside until you have made all you want to. Boil a pot of salted water, then cook the pierogies. They will float when they are done. Butter them as soon as they are taken out so that they don't stick to each other!