Combine flour and butter in large bowl. Cut in butter until mixture is crumbly.
In a separate bowl beat egg yolk and sour cream together with spoon. Add to flour mixture. Mix together well. Chill covered in refrigerator at least 4 hours. If you make this in the evening, store overnight.
Stir sugar and cinnamon together to use instead of flour for rolling dough. Sprinkle some over working surface. Roll about 1/4-1/3 of dough into circle about 10 inches in diameter, sprinkling with sugar-cinnamon mixture on both sides as needed both to roll and for taste. Cut in 16 pie shape wedges. Beginning at outer wide edge, roll toward center. Arrange on ungreased baking sheet close together, not touching.
Bake in a preheated 375 degrees F (190 degrees C) oven for 25 to 30 minutes, until browned.