In a mixing bowl, beat butter on medium speed 30 seconds or till softened. Add 1 cup of the flour, sugar, eggs, baking powder and vanilla. Beat till combined. Stir in remaining flour and nuts. Divide dough in half. (Can be done in processor).

Shape each portion into a 9-inch log (should be about 2 inches wide.) Place about 4 inches apart on lightly greased cookie sheet. For a shinier appearance, stir together egg yolk and milk/water; brush onto logs. Bake in 375F oven for 25 minutes. Cool on the cookie sheet for 1 hour.

Cut each log diagonally into 1/2-inch slices. Lay slices, cut side down, on an ungreased cookie sheet. Bake in 325F oven for 8 minutes. Turn slices over; bake 8-10 minutes more or until dry and crisp. Cool on wire rack.

In a double boiler, heat chocolate pieces with shortening over low heat till melted, stirring occasionally. Dip one end of cooled cookie in chocolate; dry cookies on rack until chocolate sets up.