In a medium bowl, combine the sugar, cinnamon and nuts. Set aside.
In a large mixing bowl, place flour, cold cubed butter and salt. Using your fingers, crumble butter within the flour until small clumps of floured butter form.
Mix egg yolks into flour mixture. Add sour cream and combine with a wooden spoon until fully incorporated, making sure to collect the dry bits from the bottom of the bowl. If need be, finish mixing with an electric mixer, but don't overmix.
Divide dough into 3 equal sized balls. Dust dough balls with flour and wrap in wax paper. Refrigerate for 3 hours or overnight.
Prepare your rolling surface by sprinkling lightly with flour.
One ball of dough at a time, roll out each one to a 9"-10" circle, about ⅛" thick. Sprinkle the full circle with ⅓ of the cinnamon, nut, sugar mixture.
With a scraper or sharp knife, cut out "slices" like a pizza, giving yourself 8-12 "slices" per circle, depending on your desired cookie size.
Press sugar mixture gently into each triangle.
Starting from the wider end (not the point), roll each piece. Transfer to a cookie sheet and shape into a ½ moon crescent shape. Repeat with all the "slices." If you'd like, dust with a light layer of powdered sugar.
Bake for 15 minutes or until golden brown. Continue until remaining refrigerated dough balls are rolled, sprinkled and rolled.
While still warm and just out of the oven, definitely dust (yes, once more, if you already did before baking) with powdered sugar.