1In large bowl, beat powdered sugar, butter and egg with electric mixer on medium speed, or mix with spoon. Stir in flour and salt. Divide dough in half. Stir cocoa into one half. Stir chocolate sprinkles into other half. Cover and refrigerate 1 hour.
2Roll half of plain dough into 9x8-inch rectangle on lightly floured surface. Repeat with half of chocolate dough; place on plain dough. Roll doughs up together tightly, beginning at long side. Repeat with remaining plain and chocolate doughs. Wrap and refrigerate at least 8 hours but no longer than 24 hours.
3Heat oven to 400ºF. Cut rolls into 1/4-inch slices. Place slices about 1 inch apart on ungreased cookie sheet. Bake 8 to 10 minutes or until set. Immediately remove from cookie sheet to wire rack.