Mix the yeast, flour, mixed spice, sugar and 1 tsp salt in a big bowl. Whisk together the milk, melted butter and egg, then tip into the flour mixture and stir until it forms a sticky dough. Tip onto a work surface and knead for about 8 mins until the dough feels soft and stretchy. Clean the bowl, then butter it. Return the dough to the bowl, cover with buttered cling film and set aside for about 1-2 hrs, or until doubled in size, or chill for up to 24 hrs. In a small pan, simmer the cranberries, mixed dried fruit, zests and orange juice until the fruit looks plump. Leave to cool.
When you’re ready to shape the stollen, heat oven to 180C/160C fan/gas 4. Tip the dough onto a surface lightly dusted with flour. Roll out to a 50 x 30cm rectangle. Grate the marzipan over the surface of the dough (this is easier to do if the marzipan is cold). Scatter the soaked fruit and half the nuts evenly over the top, then press down lightly with your hands so they stick into the dough a bit.
With a long side facing you, roll up the dough as tightly as you’re able to, like a Swiss roll (see step 1 of our step-by-step guide). Pinch the dough together to seal the open edge, then use a large knife to cut the sausage of dough in half along its length, leaving one end intact by about 5cm (see step 2). You should now have two long strips of dough to work with. Move the dough onto a large baking sheet, oiled and lined with parchment. Twist the two pieces together, turning the cut edges outwards to expose the marzipan and fruit filling (see step 3). Once twisted, connect the two ends to make a wreath shape about 26cm in diameter with a 12cm hole in the middle. Tuck one end under the other to hide the uncut piece of dough (see step 4). Cover loosely with oiled cling film and leave the bread to prove for 30-40 mins until risen by roughly a third.
Uncover the bread and bake for 40-45 mins until the dough is golden all over. You may want to rotate the tray halfway through cooking to get even results. Leave to cool on the tray for 20 mins.
Meanwhile, mix the icing sugar with enough lemon juice to make a thick but pourable icing. Drizzle over the wreath, then scatter with the rest of the nuts. Will keep in a tin, or well wrapped, for up to three days.