1. For the dough, mix 2 eggs, flour, milk and salt using the Braun Multiquick hand blender’s compact kitchen machine with the kneading hook. Process until you have a smooth dough, then rest for 15 minutes in the fridge.
2. Bring the potatoes to the boil in a pan with salted water and cook for 15 minutes. Heat the olive oil in a frying pan, add the onion and cook for 8-10 minutes.
3. Drain the cooked potatoes and then mash them with a fork. Once the mash potato has a smooth consistency, add the chopped onion, cheeses and paprika.
4. Roll out the dough on a floured surface. Using a 4-inch pastry cutter, cut into circles. Beat the remaining egg and paint the circles. Add a spoonful of filling, fold it over in half and seal the edges.
5. Place the pierogi into a pan of salted water and bring to the boil. Simmer for 3-4 minutes.
6. Finally, heat 2 tablespoons of butter in a non-stick frying pan. Add the pieriogi and cook until browned on both sides.