Sift flour onto a work surface, add the cut margarine and crumble briefly. Add salt, egg, sour cream and milk and quickly knead into a smooth dough. Leave to rest in a cool place for at least 30 minutes. Roll out the dough 2-3mm thick and cut rectangles (5x3cm). Using spaghetti doughnut molds, fry in hot fat until golden brown. Drain on paper towels and roll in the cinnamon-sugar mixture.