Mix yeast, tepid water, sugar and 1 tbsp flour (from the whole amount) and let it turn into a yeast sponge (about 30 min).
Make a soft dough by combining flour, yeast sponge, salt, baking powder and yoghurt. Beat the dough with dough hooks for 5 min. Let it rest until it doubles in size (about 1 hour).
Roll out the dough to the thickness of your small finger. Cut out squares (triangles where necessary) with a wheel cutter, then make a single cut in the middle of each piece. Leave to proof for 15 min.
In the meantime, heat the oil to 170 degrees C. Begin frying the dough, about 2 min on each side, until golden. Drain off on a kitchen towel.
Eat with cheese, sour cream, powdered sugar, jam or plain.