In large bowl, stir together flour and baking soda. With pastry cutter or two forks, cut in butter until mixture resembles coarse crumbs. Set aside. In small mixing bowl at high speed, beat together egg yolks and sugar until light and fluffy, about 5 to 10 minutes. Beat in sour cream, lemon peel, and juice. Pour about 1/3 of yolk mixture into reserved flour mixture. Stir until combined. Repeat with remaining yolk mixture. Place dough in covered container or food-storage bag. Refrigerate until firm, about 30 minutes to 1 hour. Using about 1/4 of the dough at a time, on lightly floured surface with lightly floured hands, roll small pieces of dough to form logs, each about 6 inches long and 1/2-inch thick. Shape into twists, bows, wreaths, or letters. Place on ungreased cookie sheets. Bake in preheated 350° F oven until lightly browned, about 12 to 14 minutes. Cool on cookie sheets about 5 minutes. Finish cooling on wire racks. Makes about 72 cookies.