Combine golden raisins and currants in a bowl; stir in rum. Allow to stand overnight.
Combine flaxmeal with hot water; stir until a slurry forms and set aside.
Stir together flour, xanthan gum, salt and spices. Make a well in the center of the flour mixture. Pour yeast, 1 teaspoon sugar, and half of milk into the well. Stir to combine, incorporating a little of the surrounding flour. Allow mixture to stand in a warm place for 10-15 minutes, or until foamy.
Cut 3/4 cup butter coarsely. Add butter and almond meal to flour mixture. Stir to combine, using a wooden spoon or hands. Add eggs, lemon rind, vanilla, remaining sugar and milk, and flax slurry. Combine well to make a dough. Add orange peel, almonds, raisins and currents. Knead into dough, adding a slight bit more flour, if needed, to keep dough from being too sticky.
Form dough into a ball. Allow to rest and rise in a warm place for 1 hour.
Preheat oven to 325°.
Knead dough to make smooth. Form into a rectangle about 12-inch long.
Place rectangle on a piece of parchment or a baking sheet coated lightly with cooking spray. Allow to rest and rise in a warm place for 15 minutes.
Bake at 325° for 40-45 minutes or until golden. Meanwhile melt remaining 1/4 cup butter. Brush bread with butter upon removing it from the oven. Dust liberally with powdered sugar.
Allow to cool completely.