First you need to make a ‘yeast sponge' by mixing 100g (3½oz) of the bread flour with the yeast and 1 tsp golden caster sugar in a bowl, then beat in the milk. Cover with clingfilm and leave in a warm place for 20-25 minutes until the mix has risen and looks bubbly.
Tip the rest of strong white bread flour into a large bowl with the salt and butter. Rub the butter into the flour. Stir in the mixed spice, the 50g (2oz) golden caster sugar and the dried fruit. Pour the egg into the yeast sponge, then stir this into the flour and fruit to make a dough. The dough should be soft and light, not too dry or sticky, so adjust with a little flour or water.
Tip the dough onto a lightly floured surface and knead for 5-8 minutes, dusting the work surface with more flour as needed. Put the dough back in the bowl (cleaned and lightly oiled), cover and leave in a warm place for an hour or so, until risen to about twice its original size.
Take the dough from the bowl and knead briefly. Cut the dough into 10 equal pieces. Take one piece, leaving the rest loosely covered with clingfilm, and shape into a round by bringing the edges up and pinching in the middle. Turn it over so the smooth side is on top, then repeat with the remaining pieces.
Lay the buns on 2 lightly buttered baking sheets, spaced apart so that they have room to rise. Cover loosely and leave to rise again for about 45 minutes-1 hour, or until they have risen by at least half again and feel light and puffy when gently touched. Preheat the oven to Gas Mark 6, 200°C, fan 180°C.
Meanwhile, prepare the mix for the crosses. Make a small greaseproof paper piping bag, or snip a small bit off a corner of a small plastic food bag. Mix the plain flour with 3 tbsp plus 1 tsp of water to make a thick, smooth, piping paste. When the buns have risen, spoon the paste into the piping bag and pipe crosses over each bun. Bake for 12-15 minutes until they're golden and sound hollow when tapped underneath.
For the glaze, mix together the golden caster sugar with the milk. Remove the buns from the tray and trim off any excess piping mixture from the bottom of each one. Put them on a cooling rack and brush with the sugar glaze while they are still warm. Serve warm and buttered.