Put the orange zest in a bowl and set aside. Pour the juice into another bowl, add 75ml boiling water and the dried cranberries, then leave to soak.
Meanwhile, pour the milk into a saucepan, add the butter and heat over a low heat, stirring occasionally, until the butter has just melted. Turn off the heat and beat in the egg by hand.
Mix together the bread flour, yeast, 1 tsp salt, and the mixed spice and sugar in a large bowl. Make a well in the flour and pour in the milk mixture.
Drain the cranberries and add to the bowl with the orange zest, then mix into the dough with a wooden spoon until it comes together enough to handle without getting too sticky.
Tip out onto a floured surface and knead for 5 mins until smooth and elastic – you’ll need to keep poking the cranberries into the mix as you go. Grease a bowl with a little oil, then add the dough and cover with cling film. Leave somewhere warm to rise for 1 hr.
Once risen to twice the size, turn out the dough onto a lightly floured surface. Knock it back by kneading for about 1 min – this will get all the large air holes out and give you nice even buns.
Divide the dough into 16 equal pieces, roll into balls and lay on baking sheets lined with parchment. Put a plastic bag over the baking sheets and leave to prove for 1 hr more.
Heat oven to 220C/200C fan/gas 7. Mix together the plain flour and 5 tbsp water in a bowl to a sticky consistency. Spoon into a piping bag with a small opening, or use a 2mm nozzle, and pipe crosses onto each risen bun. Put the buns in the oven for 20-22 mins until brown on top.
While the buns are baking, make the glaze. Pour the orange juice into a saucepan and mix in the jam. Bring to the boil over a low heat, then simmer for 3-5 mins – you’ll need to keep an eye on this the whole time and stir it to stop it sticking. Once the buns are cooked, put them on a wire rack and immediately paint with the glaze. Leave to cool, then eat with butter. Will keep for up to 2 days in an airtight container.