In a large bowl, combine the flour, 1 cup sugar, baking powder, baking soda and salt. Cut in shortening until mixture resembles coarse crumbs. In a bowl, whisk the egg yolks, sour cream, water and vanilla; gradually add to crumb mixture, tossing with a fork until dough forms a ball. Divide into thirds. Chill for 30 minutes. , Between two large sheets of waxed paper, roll out one portion of dough into a 15x10-in. rectangle. Transfer to an ungreased 15x10x1-in. baking pan. Sprinkle with 1-1/4 cups walnuts and 2 tablespoons sugar. Roll out another portion of dough into a 15x10-in. rectangle; place over walnuts. Spread with jam; sprinkle with remaining walnuts and sugar. , Roll out remaining pastry; cut into strips. Arrange in a crisscross pattern over filling. Trim and seal edges. Bake at 350° for 25-30 minutes or until golden brown. Cool on a wire rack. Cut into bars.