Warm the milk in the microwave or a pan until it reaches around 40'C (skin temperature). Stir in the caster sugar then add the yeast. Cover with a tea towel and sit in a warm place for 5-10 minutes until it forms a frothy head on top like a pint of beer.
Meanwhile mix the gluten free bread flour, xanthan gum and baking powder in a large mixing bow and stir together.
Crack the egg into a small bowl and add the vanilla extract. Beat with a fork until mixed. Melt the butter in the microwave.
When the yeast mix is ready, make a well in the middle of the flour and pour the yeast mixture in. Pour the beaten egg and melted butter in too.
Using a wooden spoon, beat the mixture together until it forms a thick, sticky dough. It should start to come away from the sides of the bowl but be quite stiff and sticky to mix - you'll need some elbow grease!
Lay a large piece of clingfilm (or two pieces overlapping each other) out on the work surface and very lightly oil them. Turn the dough out into the centre of them.
Wet your hands with cold water and shape the dough into a rough, flat rectangle shape. Keep wetting your hands to stop the dough from sticking to them.
Cover the rectangle with more clingfilm and then roll out the dough into a large rectangle, around 4mm thick. You can use wet hands to bring the ends back into a neat, large rectangle shape.
Once rolled out, melt the butter for the filling. Take off the top layer of clingfilm and brush the butter all over the dough in an even layer. Mix the brown sugar and cinnamon together in a bowl and then sprinkle liberally and evenly to completely cover the dough.
Using the clingfilm to help you, roll the dough from the longest edge and keep going until the dough is completely rolled up into a long cylinder shape.
Cut the dough into 12 event pieces - I do this by cutting the cylinder in half with a sharp knife, then each half in half again, then finally cut each piece into three.
Lightly oil a 24cm square tin. Lay the rolls down in the tin in three even rows of four. Cover the tin with clingfilm and then place in a warm spot and prove for 50-60 minutes. They should puff up in size and all be touching.
When the dough has proved, preheat the oven to 180'C / Gan 160'C / Gas Mark 4. Remove the clingfilm and bake the cinnamon rolls for 20-25 minutes until golden on top.
Remove from the oven and leave the rolls to cool for around 30 minutes. Make the icing by mixing the ingredients together in a bowl until smooth. Pour evenly over the rolls and leave for 5 minutes to set before tearing the rolls apart and eating them.
Notes
These cinnamon rolls are best eaten on the day of baking. You can keep them in an airtight container for a couple of days and refresh them in the microwave for 10-15 seconds before eating.
I always use the FREEE by Doves Farm gluten free white bread flour which is a mix of rice, potato and tapioca flour.
I usually use the Allinsons Easy Bake Yeast (in the baking aisle) or FREEE by Doves Farm yeast (in the free from aisle). Both are gluten free.