In a bowl, combine the orange zest, sultanas, raisins, currants, and 1 cup of brandy. Cover with plastic wrap or a tightly fitting lid and allow to steep overnight, stirring from time to time.
Preheat the oven to 300°F. Coat a loaf pan or 9-inch round pan with butter. Combine the soused fruit with 2 tablespoons of flour. In a separate bowl, combine 3/4 cup flour, nutmeg, salt, mace, cinnamon, and baking soda. In yet another bowl, whisk together the butter, sugars, and vanilla. Beat in the eggs one at a time, then stir in 1 tablespoon of brandy and the molasses. Stir the flour mixture into the wet mixture until completely combined.
Strain the fruits from any brandy that hasn't been absorbed and add them into the batter. Stir to evenly disperse, then pour the batter into the prepared pan.
Bake for 50–60 minutes, or until the fruit cake is completely done inside. Allow to cool completely before dusting with powdered sugar.