In a large bowl, mix together the flour and salt. In a smaller bowl, stir together the oil and egg, beating together lightly. Stir into the flour. It will not combine well, but keep stirring and working at it until you have a coarse meal, like biscuit dough before you add the liquid.
Pour the hot water into the flour and egg mixture all at once. Immediately start stirring. It won't look like it’s coming together, but keep stirring until it comes together into a somewhat lumpy dough. Cover with a damp tea towel or loosely cover with plastic wrap and let it rest for at least 15 minutes, preferably 30.
To make your perogies, roll the dough out about 1/4-inch thin and cut into rounds with a glass rim or round cookie cutter – or not. Cheryl rolls her dough into a long rope, cuts off 1 inch sections and then rolls each ball into a rough circle, thus not wasting any dough nor needing to reroll scraps, which can make dough tough. However you do it, fill each with a small spoonful of filling - mashed potatoes spiked with cheddar or cottage cheese, cooked bacon, or even leftover chicken and gravy - and fold over, pinching the edges to seal. Freeze in a single layer, then transfer to freezer bags, or cook (fresh or frozen) in boiling water until they float to the surface, then give them another minute. If you like, pan-fry with onions and bacon after they’re boiled and well-drained.