Beat butter at medium speed of an electric mixer until creamy; gradually add sugar, beating well. Add egg and vanilla; beat well.
Combine flour, baking powder, and salt; stir well. Add flour mixture to butter mixture, beating at low speed.
Remove half of dough from bowl. Add minced cherries to dough in bowl, and mix well. Add 3 tablespoons flour if dough is too soft. Remove cherry dough from mixing bowl, and set aside. Return plain dough to mixing bowl; add melted chocolate, beating well. Cover and chill both portions of dough 1 hour.
Roll each half of dough to a 15" x 8" rectangle on floured wax paper. Place cherry dough on top of chocolate dough; peel off top wax paper. Tightly roll dough, jellyroll fashion, starting at short side and peeling wax paper from dough while rolling. Cover and chill 1 hour.
Slice dough into 1/4" slices; place on ungreased cookie sheets. Bake at 350° for 10 to 12 minutes. Remove to wire racks to cool.
Note: To prevent flat-sided cookies, turn dough rolls halfway through the second chilling time. Dental floss makes cutting the dough easier.