- Place potatoes in a pot and cover with 2" cold water. Bring to a simmer and cook until very tender, about 18 to 20 minutes.
- While potatoes cook, melt 2 Tbsp. butter in a small skillet set over medium heat. Add the onion and cook until tender, about 4 to 5 minutes.
- When cooked, drain potatoes well and then thoroughly mash until very smooth (you should have about 3 cups). Add the cooked onion and cheese and mix until cheese is melted and well blended in. Cool potato filling to room temperature.
- Make dough by placing egg in a large bowl and beating well. Mix in the oil, water and salt. Mix in 21/2 cups of the flour until loose dough forms. Sprinkle 1/4 cup flour on a work surface. Coat your hands with flour and shape and knead the dough into a small ball, adding additional flour if needed. Cut dough in half and press each piece into a thick disc. Now wrap each dough and let rest 30 minutes to relax the gluten.
- To make perogies, set one piece of dough on the floured surface. With a floured rolling pin, roll dough until about 1/8" thick. Use a 3" round biscuit cutter to cut dough into rounds.
- Put one of the rounds in the palm of your hand. Place a walnut-sized ball of the potato filling in the centre of the dough round. Fold the dough over the filling and firmly press the edges together. Set perogie on a large parchment paper-lined baking sheet. Fill remaining dough rounds as you did the first. Do not let perogies touch when setting them on the baking sheet.
- Roll out the second dough and cut and fill it as you did the first. Also form the scraps of dough into a ball and roll, cut into rounds and fill them too.
- To cook, bring a large, wide pot of lightly salted water to a boil. Preheat the oven to 200˚F. Boil perogies 8 or so at a time, stirring occasionally so they don’t stick, 4 to 5 minutes, until the dough is cooked and puffed slightly.
- Lift cooked perogies out with a slotted spoon, drain well, and then arrange in wide, ovenproof dish. Brush the top of perogies with the melted butter and then keep warm in the oven. Cook the rest of the perogies in this fashion, adding them to the dish and buttering them as you go along. When all are cooked, sprinkle with green onion and serve with sour cream.
Note: You could also serve the perogies with chopped cooked bacon and sautéed onions.
Recipe Options: After forming, the perogies, uncooked, could be frozen solid on the baking sheet, transferred to freezer bags and kept frozen. When needed, boil them from frozen, adding a minute or so more to the cooking time. For golden brown perogies, after boiling and draining them, fry them a few minutes on each side in melted butter.