Mix together the raisins, sultanas, cranberries and rum. Cover and set aside to soak. Ideally you should do this the day before you want to bake the stollen.
To make the dough, mix together the bread flour, instant yeast, salt, sugar, cardamom, cinnamon, nutmeg and allspice in a large bowl or in the bowl of a stand mixer fitted with a dough hook.
Add the finely grated orange and lemon zest and the lukewarm non-dairy milk. Mix to form a rough dough then knead either by hand or with the mixer until the dough is smooth.
Gradually knead in the softened butter, a little at a time, until it is all incorporated. Continue to knead the dough until it is smooth and elastic. It should be slightly sticky but if it seems too wet you can add a little more flour.
Place the dough in an oiled bowl, cover and set aside to rise in a warm spot until it is doubled in size, about 1 ½ – 2 hours. Alternatively, you can prepare the dough in the evening and place it in the fridge to rise overnight then continue with the recipe in the morning.
Once the dough has risen, add the soaked fruits and the chopped almonds. Knead the dough until they are evenly distributed.
Divide the dough into two equal halves (I use a scale for accuracy). Roll one half out on a lightly floured surface into a narrow rectangle, about 45cm / 18in long.
Roll one half of the marzipan out into a sausage just very slightly shorter than the rectangle of dough. Place it on top of the dough then roll the dough up from one of the long sides into a sausage, fully encasing the marzipan.
Use your hands to roll the sausage out until it is about 60cm / 24in long then repeat these steps with the other half of the dough and marzipan.
Cross the two ropes of dough in the middle then twist them together. Shape the twist into a wreath and pinch the ends together to seal.
Place the wreath on a baking parchment lined baking sheet, loosely cover and set aside to rise until it is puffy, about 1 – 1 ½ hours.
When the wreath is nearly ready, preheat the oven to 180°C/160°C fan/350°F/gas mark 4.
Pick off any fruit from the surface of the wreath as they will burn in the oven, then bake for 45 minutes. If the top of the stollen starts to get too dark before it is cooked through, loosely cover it with tin foil.
When it is ready a probe thermometer inserted into the centre (but not into the marzipan) should read 94°C/201°F.
Brush the baked stollen liberally with melted butter then carefully slide it onto a wire rack to cool completely. Dust the top with icing sugar once the butter has set and again just before serving.