Chocolate-Vanilla Pinwheel Cookies

1 cup butter
1 1/2 cups sugar
1 1/2 tsp baking powder
1/4 tsp salt
1 egg
1 tsp vanilla
2 1/2 cups flour
2 oz. unsweetened chocolate melted

Beat butter on high for 30 seconds. Add sugar, baking powder, and salt and beat until combined. Beat in egg and vanilla until combined and then mix in flour. Divide dough in half. Add chocolate to one portion of dough. Roll out chocolate dough between sheets of waxed paper into rectangle shape about 1/4 in. thick. Roll out plain dough and place on top of chocolate dough. Roll up jelly-roll style (Lengthwise) and wrap in plastic wrap. Chill dough for at least 2 hours. Cut roll into 1/4 in. slices and bake on ungreased cookie sheet for 7 to 9 min. at 375. Do not overcook.