Mix the flour, salt and cold butter, rub with your hands until crumbs.
Add sour cream and knead the dough (by hand or in a combine with a dough nozzle).
Wrap in plastic wrap and put in the refrigerator for 30 minutes.
Divide the dough into two parts. Each part, in turn, thinly (1-2 mm) roll out in a rectangular layer.
Roll the dough into a roll.
Roll the roll several times to make the seam stick together well.
Cut into "cubes" of about 10 cm and the top side, where there is no seam, dip in sugar.
Place on a baking sheet lined with parchment paper, sugar side up, seam down.
Bake in a preheated (150-160) oven for about 30 minutes.