Add the milk, water and brown sugar to a microwave proof jug or small pot and heat until warm to the touch (about 45°C/110°F) Whisk well to dissolve the sugar. Pour into a large bowl, or the bowl of a stand mixer, sprinkle the yeast on top, stir in and leave to sit for 5 minutes.
While you are waiting, combine 2 ½ cups of flour, salt, cinnamon, mixed spice, nutmeg, raisins/currants and mixed peel in a large bowl and whisk together.
In another small jug melt the butter, add the egg and vanilla and whisk together until all ingredients are incorporated.
Once the yeast has started to bubble, add the flour mixture and butter mixture to the yeast mixture and using the dough hook attachment on your stand mixer, knead for 7-8 minutes until the dough springs back when you press it. If kneading by hand, combine the dough with a wooden spoon and then turn it out onto a lightly floured surface and knead for 10 minutes. Add a little more flour if the dough is really sticky.
Cover the dough in gladwrap or a clean tea towel and leave to rise in a warm place for 60-90 minutes or until doubled in size.
Once the dough has risen, punch it down gently and turn out of the bowl onto a lightly floured surface. Split the dough into 10 evenly sized pieces roll into balls and place on a baking tray lined with a silicone liner or baking paper, so that they are almost touching. Cover with gladwrap that has been lightly sprayed with cooking oil and leave to rise in a warm place for 40 minutes.
Pre-heat the oven to 180°C/350°F.
While the buns are rising, make the mixture for the crosses. In a small bowl whisk together milk, flour and sugar until smooth. Once the buns have risen, pipe the crosses on the buns, by putting the cross mixture into a piping bag or ziplock bag with the corner snipped off. If you don't have a piping bag or ziplock bag, you can carefully drizzle it with a spoon.
Bake the buns for 20-25 minutes, until the tops are golden brown. While the buns are baking, prepare the glaze by mixing the sugar and water in a small bowl and microwaving until the sugar has dissolved.
Remove from the oven and brush the buns with the sugar glaze and allow them to cool slightly.
To serve, slice the buns in half, spread with butter and enjoy!
Buns will keep in an airtight container for 3 days or can also be frozen. They are definitely best served the day of baking but you can zap them in the microwave or toast them on day 2 or 3 and they're almost as good!