Place the milk and butter in a small saucepan and heat over a low heat until the butter just melted (you don’t want the milk to be too hot - see note 1).
In a mixing bowl, stir the flour, yeast, white sugar, mixed spice and salt together. Stir in the beaten egg and then the tepid-warm milk.
Bring together to make a soft dough then knead for 5-7 until smooth and elastic (or see note 2).
Cover with a tea towel and leave in a warm place for 1 – 1 ½ hours, until doubled in size.
Tip the dough out on to a lightly floured board and roll into a rectangle 20 x 30cm.
Spread over the softened butter, then sprinkle the sultanas evenly over the surface. Mix the brown sugar and cinnamon together and then sprinkle this mixture all over the dough in an even layer.
Press down the long side closest to you to the board. Take the opposite long edge roll tightly towards you.
Cut the roll into 9 even pieces, around 4-5cm thick.
Line the bottom only of a 20 x 20 cm square tin with baking paper and place the swirls, cut side facing up, into it, leaving an even gap in between them all.
Lay a tea towel over the top and leave in a warm place for 30-40 minutes until the buns have grown in size and are now touching.
Preheat the oven to 180 ˚C fan / 360 ˚F.
Bake the buns for 20-25 minutes, checking after 15 minutes and if starting to brown and the sultanas starting to catch, cover with foil.
Leave to cool in the tray for 5 minutes.