To make the dough, heat the milk and butter in a saucepan until the butter has melted. Take off the heat.
Add the flour to a large bowl and mix in the sugar. Add the salt on one side of the flour and the yeast on the other side. Make a well in the centre, pour in the egg and then add the milk mixture. Roughly mix using the back of a spoon or a palette knife, then get your hands in and bring the dough together.
Knead the dough on a lightly floured surface until it is smooth and stretchy. This will take about 10 minutes or it can be done in a mixer with a dough hook attached, which should take about 6 minutes on a medium speed. Pop the dough into a greased bowl and leave to rest in a warm place for about 1½ hours or until doubled in size.
Line a large baking tray or 2 smaller trays with some baking paper. Tip the dough out onto a lightly floured surface and knock back the dough. Spread the dough out into a circle and sprinkle on the cranberries, blueberries and orange zest, then knead until the fruit is evenly distributed.
Take the dough and divide into 15 portions. Shape each piece into a ball and roll until it has a smooth surface. Place on the tray or trays with about a 3cm/1¼in gap between each one to give them space to prove and grow. Leave in a warm place, covered in some greased cling film, for about 40–60 minutes or until doubled in size.
Preheat the oven to 200C/180C Fan/Gas 6. To make the flour paste for the crosses, pound the strawberries in a pestle and mortar or blitz in a food processor until you have a fine pink dust. Add this to a bowl with the flour and 6 tablespoons of water and mix to a smooth, pipeable paste. Spoon into a piping bag. Uncover the proven buns and pipe a thin cross on each bun.
Bake the buns for 18–20 minutes. As soon as they are golden brown and bounce back when touched, take them out of the oven and leave to cool on a wire rack.
Use the handle of a teaspoon or the end of a cutlery knife to make a hole in the side of each bun without going all the way through. Pop the jam into a piping bag and pipe into the hole of each hot cross bun until full. You will know when it is full as the piping bag will naturally force itself out. Put the buns back onto the tray. Brush the warmed syrup all over the buns to give a sweet, sticky glaze. Filled, fruity and ready to eat!