Anise Walnut Biscotti

Preheat oven to 375 degrees F ( 190 degrees C ). In a large bowl, cream together butter and sugar. Gradually add the vanilla and eggs while mixing. Sift together the flour and baking powder; stir into the egg mixture . For plain biscotti, do not add anything else. For anise biscotti, add the anise extract and anise seed. Add walnuts if desired. Roll dough out into 4 logs as long as your baking sheet will allow. Press down each one to about 3/4 inch in height, and 3 inches wide. Brush with egg yolks and bake for 15 minutes, until golden brown. Slice on a diagonal slant, slices should be about 3/4 inch wide. Place slices back onto the cookie sheet and return to the oven for 10 more minutes, cookies should be dry and lightly toasted.