Beat butter in a large mixing bowl with an electric mixer on medium to high speed for 30 seconds. Add sugar, baking powder, and salt; beat until combined. Beat in egg and vanilla. Beat in as much of the flour as you can with the mixer. Stir in remaining flour with a wooden spoon.
Remove one-third of the dough; stir cocoa powder and milk into this third. Divide chocolate dough in half; on waxed paper shape each half into a log about 3/4-inch in diameter and 8-inches long. Set aside.
Stir enough golden yellow paste food coloring into remaining two -thirds of dough to make it golden. Divide golden dough in half. On waxed paper pat each half into an 8x4-1/2-inch rectangle. Wrap each golden rectangle around a chocolate log. Wrap rolls in waxed paper and chill for 2 to 4 hours or until firm. Using the pointed end of a bottle opener or the tip of a vegetable peeler, make six lengthwise indentations about 5/8 inch apart going to, but not through, chocolate layer.
Using a sharp knife, cut into 1/4-inch-thick slices. Place slices 2 inches apart on an ungreased cookie sheet. If desired, sprinkle golden dough with yellow decorating sugar.
Bake in a 375 degree F oven for 7 to 8 minutes or until edges are firm and light brown. Cool on cookie sheet for 1 minute. Transfer to wire racks to cool completely. Makes about 48.