In small bowl, combine raisins and the 1/2 cup rum.
Let stand, covered, several hours or overnight.
In large bowl, cream butter and sugar.
Beat in eggs, one at a time.
In another small bowl, combine flour, baking powder, spices and salt; stir into creamed mixture with raisin-rum mixture, ginger and walnuts.
Spoon batter into 8 1/2 X 4 1/2 x 2 1/2-inch loaf pan that has been lined with greased parchment paper.
Bake in preheated 250CF oven 1% to 2 hours or until pick inserted in center comes out clean.
Cool completely, then loosen edges and remove from pan.
Gently peel off paper.
Wrap cake in rum-soaked cheesecloth, then plastic wrap and store in a cool, dry place to age several weeks or longer.
Check cake occasionally and sprinkle with additional rum as needed to keep cake moist.
Before serving, garnish, if desired.