Preheat oven to 375 degrees F. Cream butter and sugar, add eggs one at a time and beat until fluffy. In a separate bowl, combine dry ingredients and add to egg mixture alternately with buttermilk, until blended. Fold in raisins, orange zest, rosemary, and walnuts. Grease mini-muffin tins and spoon batter into cups, filling halfway. Bake for approximately 15 minutes. Cool on rack for 10 minutes and remove from tins.
Maple Onion Jam:
Cut onion in half and slice thinly. Heat oil in pan, add onions, turn down heat, and cook slowly until onions are golden brown. Remove from heat and let cool. Coarsely chop onions, and stir in maple syrup.
Slice each muffin in half. Spread both cut sides of muffin with maple onion jam. Fold a strip of turkey, place on muffin half, and replace top.