In large bowl, mash hard-cooked egg yolks; combine with uncooked egg yolks and powdered sugar. Add butter and vanilla; blend well. Add flour; mix well. Cover with plastic wrap; refrigerate 2 to 3 hours for easier handling.
Heat oven to 350°F. On lightly floured surface, roll out 1/4 of dough at a time into 12-inch rope. Cut rope into 12 equal pieces. Roll each piece into 6-inch rope; shape each into wreath, overlapping 1/2 inch from ends. Place 1 inch apart on ungreased cookie sheets. Brush with egg white; decorate each wreath with 1 red cherry piece and 2 or 3 green cherry pieces.
Bake at 350°F. for 8 to 14 minutes or until edges are light golden brown. Remove from cookie sheets.