Beat sugar and sour cream until light and well mixed. Beat in eggs one at a time. Add just enough flour to form a soft dough. Wrap dough in plastic wrap and chill for 20-30 minutes.

Roll dough on a floured surface to 3/4 inch thick and cut with floured cutter (or if you don't have a doughnut cutter, cut around the bottom of a glass to get a circle and cut out a center hole). Do not handle the dough more than necessary or it will become tough.

Heat oil to 350° F. Fry doughnuts in oil, turning once, until golden brown on both sides. Drain on paper towels and roll in sugar.