In a large mixing bowl, beat the butter with an electric mixer on medium to high speed about 30 seconds or until softened. Add the sugar and baking powder. Beat until combined, scraping the sides of the bowl occasionally. Beat in the egg and vanilla. Beat in as much of the flour as you can with the mixer. Using a wooden spoon, stir in remaining flour.
Place half of the dough in a small mixing bowl. Stir in the pecans or almonds; set aside. To the remaining dough, knead in the orange peel and food coloring. Cover and chill both portions of dough about 30 minutes or until easy to handle.
On a lightly floured surface, shape each dough portion into a 12-inch-long log. Cut each log into twenty-four 1/2-inch-thick pieces. Roll each piece into a 6-inch-long rope. If necessary, cover and chill ropes for 10 to 15 minutes if soft and difficult to work with. Place a white and an orange rope side by side and twist together 5 or 6 times. Shape into a circle, gently pinching together the ends. Place on an ungreased cookie sheet. Repeat with remaining dough, leaving 2 inches between cookies. Bake in a 375 degree F oven for 8 to 10 minutes or until edges are light brown. Cool on cookie sheet about 1 minute, then remove and cool thoroughly on a wire rack.
In a small mixing bowl, stir together sifted powdered sugar and enough milk to make an icing of piping consistency. Tint with desired colors of paste or liquid food coloring.
Using a decorating bag and writing tip #2, pipe icing into various-size spiders randomly on cookies. If desired, use red cinnamon candies, or candy-coated chocolate pieces for the body of the spider. Use a dab of icing to hold body on cookies. Let cookies stand until icing is set. Makes 24 cookies.