With a wooden spoon, beat the soft butter and cottage cheese together in a bowl until smooth. Add the flour and baking powder, and knead to make a soft dough.
Roll the dough between your palms into a ball, then roll it out with a rolling pin to a thickness of 5-6 mm. Using a glass or cookie cutter measuring about 8 cm in diameter, cut out as many circles as possible. Gather any leftover dough and repeat the process.
Preheat the oven to 180°C (356°F). Pour the sugar onto a flat plate. Gently press one side of the circle of dough into the sugar. With the sugar-coated side always facing inwards, fold the circle in half. Press the semicircled dough into the sugar and fold the dough in half again to form a triangular shape. Repeat with the rest of the dough.
Place the cookies on a baking sheet lined with parchment paper, spacing them about 2 cm apart. Bake on the middle rack of the oven until the cookies are golden, about 35 minutes.