Soak the dried fruit (the day before): The day before baking, chop the dried fruit into smaller pieces (about the size of raisins). Add the chopped dried fruit and 1/2 cup spiced rum into a large bowl. Stir the mixture, cover the bowl and let the mixture sit overnight on the counter.
Roast the nuts: Preheat the over 350°F. Spread your nuts on a cookie tray and roast them in the over for 8-10 minutes or until fragrant and golden. Take the nuts out to cool. Chop the nuts coarsely and set them aside.
Make the fruit cake: Preheat the oven to 250°F and prepare two 9 by 5 inch or six 5 by 3 inch loaf pans by buttering and lining them with parchment paper.
Separate the eggs ensuring that is no egg yolk in the egg white. If there is any egg yolk in the egg whites they will not whip up properly.
In a large mixing bowl or stand-up mixer, cream together the butter and sugar until light and fluffy. Add the egg yolks and beat until well combined.
Mix the flour, spices and salt (if using) in a medium sized bowl and then add the flour mixture to the butter mixture. Mix until combined.
Before adding the dried fruit and roasted nuts remove the bowl from the mixer. Most mixers won't be able to mix such a large volume of dried fruit and nuts and you might break your mixture by trying. Add the rum soaked dried fruits and roasted chopped nuts to the dough and mix with a study wooden spoon.
In a medium clean bowl, beat the egg whites until stiff peaks form. Gently fold the beat eggs whites into the thick dough mixture with a wooden spoon.
Divide the dough evenly between the prepared bread pans and place them into the preheated oven.
Bake large sized loaves (9 by 5 inch) for 3 or 3.5 hours and the small loaves (5 by 3 inch) for 2.5 to 3 hours. Use a wooden skewer or toothpick to check the middle of the cake for doneness, it should come out clean when ready.
Cool the fruit cakes on a wire rack for 15 minutes and then remove from them from the pans. Let them fully cooled to room temperature.
Age the fruit cake: Winter fruit cake can be eaten right away but it tastes much better after one or two weeks of aging. To store the fruit cake brush the loaf generously with spiced rum and then wrap each loaf separately in rum soaked cheese cloth. To soak the cheese cloth place it in a bowl and pour spiced rum over it until damp but not dripping wet. Then wrap each loaf in plastic and store them in a cool dark place.