How to make pierogies
Mix flour and salt. In a separate bowl, combine the egg and oil. Then, stir into the flour mixture until it forma a coarse meal.
Add very hot (boiled) water. Stir until it just comes together - don't overmix!
Cover lightly with plastic wrap and let sit, 30 minutes.
Roll dough into ball. Roll out onto a lightly floured surface and cut circles with a glass or cookie cutter.
Mix your fillings! I used: mashed potatoes and cheddar cheese, ricotta with lemon and thyme, and a plain ricotta cheese. Be liberal with the salt, pepper and seasonings!
Put about 1 teaspoon of filling in the center of each circle of dough and pinch close. Careful to not overfill! I closed each type differently to differentiate.
Place on parchment paper on a baking sheet and freeze. Cool or store as you normally would!