Directions:

To make dough:
Place flour and salt in a food processor and process a few seconds. Add butter. Pulse about 10 times until butter is about the size of a pea. Add egg yolk and sour cream. Turn on the processor and let it run until the mixture just starts to form a ball. Pour out mixture onto a sheet of plastic wrap and use your hands to form into a smooth 6 inch disc. Dust with flour, wrap well and chill for at least 1 hour and up to several days.

To assemble:
Prepare 2 cookie sheets by covering with parchment paper. Heat oven to 350 degrees (if using a convection oven, set heat at 325 degrees). Have bowls of sugar and walnuts at hand and a pastry brush for the jam.

Cut the dough into 3 equal pieces for larger rugalach or 4 equal pieces for smaller rugalach. Take one piece and form into a circle. Dust a pastry board with flour and lightly dust the dough also. Roll out the dough into a circle until thin. Brush the dough with a thin layer of jam. Sprinkle on about 3 tablespoons of the sugar and then 1/3 or 1/4 cup of the nuts. Press the nuts down into the dough with your hands. Cut the circle of dough into 12 wedges and roll each piece starting from the big end.

Place each cookie on the cookie sheet, with the point down, about an inch or two apart. Keep in the refrigerator until you have a whole sheet filled. Bake 25-30 minutes until nicely browned. Cool on baking racks. Dust with powdered sugar before serving. Can be stored in airtight tins.