Combine first 4 ingredients in a small bowl; set aside.
Beat butter and sugar in a large mixing bowl at medium speed with an electric mixer until creamy. Add flour mixture and buttermilk alternately to butter mixture, beginning and ending with flour mixture; beat at low speed after each addition just until blended. Stir in vanilla. Add egg white, mixing well.
Fill cones to within 1/2 inch of the top; carefully place on an ungreased baking sheet. Bake at 375 degrees for 35 minutes; cool completely on wire racks. Spread evenly with Frosting. Top with colored sprinkles and a cherry, if desired.