Isn't there some confusion here between Christmas cake and plum pudding? The former, packed with sultanas, raisins and currants, is eaten cold at 'tea time' while the latter, with the same fruit but a lot of suet, is eaten hot with sauce, as the dessert for Christmas dinner? Christmas cake has a covering of marzipan and icing. The poem seems to be referring to cake with its 'snowy round' rather than pudding though the latter is more 'odorous'.