Combine golden raisins, dried currants, candied orange peel, and candied lemon peel in a bowl. Pour in dark rum and stir to coat. Cover and soak overnight or at least 4 hours. Drain before using.
Combine warm milk with 1 teaspoon of sugar, then sprinkle yeast on top. Let stand for 8-10 minutes until foamy and fragrant.
In stand mixer with dough hook, combine flour, remaining sugar, salt, cardamom, cinnamon, nutmeg, lemon zest, and orange zest. Add eggs, vanilla, and yeast mixture. Mix for 2-3 minutes until a shaggy dough forms.
With mixer on low, add softened butter one tablespoon at a time, waiting until each piece is mostly incorporated. Once all butter is in, knead on medium for 5-7 minutes until smooth and elastic.
Shape dough into a ball, place in greased bowl, and cover. Let rise in warm place for 1-1.5 hours until doubled in size.
Turn dough onto floured surface. Press into rough rectangle, scatter drained fruit and almonds over top, then fold and press until evenly distributed throughout.
Knead marzipan briefly to soften, then roll into a 10-inch log about 1 inch in diameter.
Roll dough into 12x8 inch oval. Press a shallow groove slightly off-center. Place marzipan log in groove and fold larger side over to seal. Transfer seam-side down to parchment-lined baking sheet.
Cover shaped Stollen and let rise for 45 minutes to 1 hour until puffed but not doubled. During last 15 minutes, preheat oven to 350°F (175°C).
Bake for 45-55 minutes until deep golden brown and internal temperature reaches 190-195°F (88-90°C). Tent with foil if browning too quickly.
While still hot, brush generously with melted butter. Apply 3 coats total, waiting 2-3 minutes between each. Once completely cool, sift powdered sugar heavily over entire surface.
Wrap cooled Stollen tightly in plastic wrap then foil. Store at cool room temperature and rest at least 2 days before slicing for best flavor development.