Grease an 8- to 9-inch cake pan. Add chips, condensed milk and vanilla to a large, heavy pot over low heat and melt. Add currants and walnuts.
Wrap the empty condensed milk can with plastic and place in the center of the cake pan. Fill pan with fudge. Do not smooth the top – let the wreath be bumpy and irregular on the surface.
Decorate with cut red and green cherries to look like holly bunches and chill. Remove from pan, remove can, place on a platter and serve in very thin slices.