2) For the dough, place both the flours in a large bowl, add the baking powder and salt and mix well. In a separate bowl place the egg, olive oil and 240ml of water and whisk until combined.
3) Add the wet ingredients to the dry ingredients using a wooden spoon to form a ball. Cut the dough in half. (You can freeze it for another time, if desired.)
4) Flour a work surface and roll the dough about 3mm thick. Use a 7 1/2cm biscuit cutter to cut out 12 rounds from the dough.
5) Place a dollop of filling in the centre of each dough round. Fold the dough over the filling to form a half moon. Press the edges together with your thumb and seal using the flat tines of a fork.
6) Bring a large saucepan of salted water to a simmer. Add the perogies and cook for about 2 minutes, then drain.
7) Meanwhile, in a large frying pan over a high heat, melt half the butter and add the onion. Cook for 5-6 minutes until slightly caramelised.
8) Add the perogies and the remaining butter. Allow to saute for a few minutes, then add the spring onions.
Remove to a serving platter and serve with sour cream.