Bring a large pot of water to a boil and add in your cubed potatoes. Cook until potatoes are soft and a fork can easily cut through.
While the potatoes are cooking, sauté the onions a pan with a bit of olive oil until translucent.
Drain potatoes and let stand for 5 minutes while the excess moisture evaporates from the potatoes, then mash.
Mix together the potatoes, onions, cheese, paprika, garlic powder, onions powder and salt.
Preheat the oven to 375 degrees. Lay out one sheet of phyllo pastry and lightly brush with olive oil. For more pastry in each bite, you can use two sheets.
Spread a thin layer of filling over half of the lightly oiled phyllo sheet. Start rolling up your sheet to make a long bar shape and then twist in to a swirl.
Repeat the to continue the swirl until your pie dish no longer has room in it (4 rolled sheets with filling). You can also use a cookie sheet and make smaller individual portion sized swirls (1 rolled sheet with filling each).
Brush the top of your swirl with egg yolk and bake until golden brown. (around 30 minutes)
Cut your Borek as you would a pizza or a pie and serve warm, as a side dish, an appetizer or the main course!