Make the dough first. Heat the milk in a pan until steaming. Remove from the heat, and drop in the butter. After a couple of mins, beat in the egg and half the orange zest.
The liquid should be just warm for step 2.
Mix the strong flour, yeast, 1 tsp salt and the sugar in a large bowl, then tip in the liquid and stir to make a soft dough without dry patches. Flour the work surface and your hands, then knead the dough for 5-10 mins until smooth and elastic. Use a stand mixer or processor if you like. Oil a large bowl, sit the dough inside it, then cover with oiled cling film. Rise in a warm place for about 1 hr or until doubled in size.
Put the raisins and half the orange juice in a small pan or covered bowl, and either simmer for a few mins or microwave on High for 1 min until hot. Cool completely. Break the chocolate into a food processor with the cinnamon and 2 tbsp sugar, then pulse until very finely chopped. Mix in the rest of the zest. If you don’t have a processor, chop it by hand or grate it, then mix with the other ingredients.
Turn the risen dough onto a floured surface and press it out to a large rectangle, a little bigger than A4 paper. Scatter it evenly with the chocolate mix and the raisins, which should have absorbed all of the juice (drain them if not). Roll the dough up around the filling, then knead it well for a few mins until the chocolate and fruit are evenly spread. Some raisins and chocolate will try to escape, but keep kneading them back in.
Grease then line a large baking sheet with baking parchment. Divide the dough into 12 equal pieces. Shape into buns by pinching each ball of dough into a purse shape, concentrating on making the underneath of the ball (which will be the top) as smooth as you can. Put the buns, smooth-side up, onto the baking sheet, leaving room for rising. Cover loosely with oiled cling film and prove in a warm place for 30-45 mins or until the dough has risen and doesn’t spring back quickly when prodded gently.
Heat oven to 190C/170C fan/gas 5. To make the paste for the crosses, gradually stir 6-7 tbsp water into the plain flour to make a smooth, thick paste, then put in a food bag and snip off the end to about 5mm. Pipe the crosses, then bake for 20-25 mins until the buns are risen and dark golden brown.
Mix the rest of the orange juice with the remaining sugar and let it dissolve. Brush the syrup over the buns while they are hot, then leave to cool. Eat on the day of baking, or toast the next day.