In a large bowl, beat the butter and sugar until light and fluffy. Beat in the eggs, one at a time, mixing until smooth. Combine the flour, salt and baking powder, then stir into the creamed mixture. Fold in the chopped walnuts and aniseed. Shape the dough into 4 or 5 rolls that are the same length as the baking tray. Place the rolls onto ungreased baking trays and flatten slightly.
Bake for 15 to 20 minutes in the preheated oven, until just starting to brown. Remove from the oven and cool on wire racks. When the rolls are cool enough to handle, transfer them to a cutting board. Using a serrated knife, cut the rolls crossways into 2.5cm slices. Place the slices cut-side down on the baking trays and return to the oven for an additional 5 to 10 minutes more, until golden and crispy.
Oil can be used in place of butter or margarine for a lower fat version. Any type of nuts can also be used in place of the walnuts.