Line 2 cookie sheets with parchment paper or light grease the cookie sheets; set aside. In a large bowl beat butter with an electric mixer on medium to high speed for 30 seconds. Add granulated sugar, baking powder, and 1/2 teaspoon salt; beat until combined, scraing side of bowl occasionally. Beat in eggs, lemon peel, and vanilla until combined. Beat in as much of the flour as you can with the mixer. Using a wooden spoon, stir in any remaining flour and the pistachio nuts.

On alightly floured surface, divide dough into 3 portions. Shape each potion into an 8-inch-long loaf. Place loaves at least 3 inches apart on prepared cookie sheets. Flatten loaves to about 2-1/2 inches wide. Bake in a 375 degree F oven for 20 to 25 minutes or until golden and tops are cracked. (Loaves will spread slightly.) Let stand on cookie sheets on wire racks for 30 minutes. Reduce oven temperature to 325 degree F.

Transfer loaves to a cutting board. Cut each loaf diagonally into 1/2-inch-thick slices. Place slices, cut sides down, on the same parchment-lined or greased cookie sheets. Bake in a 325 degree F oven for 8 minutes. Turn slices over and bake 8 to 10 minutes more or until dry and crisp. Transfer to wire reacks; cool. For icing, stir together powdered sugar and enough lemon juice or milk (1 to 2 tablespoons) to make icing of drizzling consistency. Drizzle over biscotti. Let stand until frosting is set. Makes about 36 cookies.

Prepare Lemon-Nut Biscotti as directed through Step 3, except do not drizzle with icing. Transfer to self-sealing freezer bags or arrange in layers separated by waxed paper in a freezer container. Seal, label, and freeze up to 3 months.

To serve, thaw biscotti at room temperature 15 minutes. Drizzle with icing.