Place the milk and yeast into a bowl and mix well. Leave to sit for 5-6 minutes.
Meanwhile, sift the salt, sugar, flour and mixed spice into a large bowl. Add the dried fruit, almonds and butter and mix well then stir in the yeasty milk and mix well.
Add the egg and stir to form a dough. Knead the dough for 5-6 minutes, then cover and leave to prove for 20 minutes. .
Uncover the dough and turn out onto a clean, floured work surface. Knock the dough back to reduce the volume, then knead the dough for 3-4 minutes
Push the dough out by hand into a flat oval shape about 23cm x 18cm/9in x 7in. Roll the marzipan into a sausage shape about 6cm/2in shorter than the dough. .
Place the marzipan into the centre of the dough, then fold over the sides of the dough to seal in the marzipan. Then fold in the ends of the dough to contain the marzipan and help give the dough shape
Place the stollen seal-side down onto a greased baking tray. Cover and place somewhere warm to prove for one hour.
Preheat the oven to 180C/365F/Gas 4. Place the stollen on the baking tray into the oven to bake for 40 minutes, or until golden-brown and cooked through.
To finish, remove the stollen from the oven, brush with the rum then melted butter and dust liberally with icing sugar immediately. Allow the stollen to cool, then serve in slices.