Preheat oven to 350 degree F. Line cookie sheet with parchment paper. Beat butter with mixer on medium to high speed 30 seconds. Add sugar, soda, baking powder, and salt; beat until combined. Add eggs, lemon peel and juice, and extract. Beat until combined. Add flour; beat until combined. Stir in nuts. Divide dough in half. Shape each into a 12-inch roll. Place at least 3 inches apart on baking sheet. Bake 35 to 40 minutes or until beginning to brown (logs will spread). Cool completely on a rack. Use a serrated knife to cut each roll into 3/4-inch slices. Place, cut sides down, on ungreased cookie sheet. Bake in 350 degree F oven for 5 minutes. Turn slices over; bake 5 minutes more or until dry and crisp. Cool on rack. Dip 1 end of biscotti into white chocolate; sprinkle with nuts. Dry completely. Makes 36 biscotti.
Combine pistachio nuts and macadamia nuts. In small saucepan melt white chocolate baking squares over low heat. Stir in lemon peel and shortening. Add additional shortening, 1 teaspoon at a time, until of dipping consistency.