In a large bowl, sift the flour, add a pinch of salt, the sweet paprika and the baking powder. Mix to combine.
Add the egg and the milk and mix until getting a stiff dough. Shape into a ball, cover with kitchen foil and let it rest in a warm place for around 2 hours.
Meanwhile, add 4 tbs oil to a frying pan and fry the meat for a few minutes (stirring constantly).
Add the onions and leeks, season with salt and pepper, continue frying until the onions are doft and the meat is cooked through.
Rool the pastry out in a floured surface and cut triangles out of it.
Place a tablespoon of the meat mixture in the center of the triangle and fold over to form a samboussa.
Heat oil in a wok until almost smoking and place the samboussas one at the time in this.
Cook until golden brown and crisp on all the sides, remove with a slotted spoon and drain on kitchen paper.
Allow to cool down a little and serve.