In a large bowl, mix all the flours, starch, coconut sugar, vanilla sugar and cinnamon.
Chop the butter into small pieces and add to the dry ingredients, rubbing it in until it resembles breadcrumbs.
Beat the egg and then stir in to the other ingredients until combined. Leave the mixture for a few minutes to see whether any water is required (coconut flour soaks up liquid like a sponge, which is not always apparent when it is initially added). The mixture should pull together as a workable dough - if it is crumbly, add a teaspoon of cold water one at a time, just until the right consistency is achieved.
Divide the mixture into two roughly equal bits, and roll each one out on baking paper sprinkled with a little sorghum flour (you may need to place another piece of the top if it becomes too sticky). Don't worry about rolling it out nice and accurately, it's supposed to be rustic.
Place the strawberries in the middle part of the pastry, leaving a gap all the way around. Make sure there isn't too much juice, as this will make the pastry soggy (I poured some off and used it to drizzle over Greek yoghurt before serving).
Gently pull the outer edges up over the fruit (again, it doesn't have to be perfect). The pastry can be a little tricky, so if cracks or holes develop, just pinch the pastry together to seal them.
Top each one with a large blackberry (entirely optional, but it gives the galettes a little contrast in colour).
Sprinkle with a little coconut sugar and bake for around 25-30 minutes, until the pastry has browned and the fruit mixture is bubbling.
Remove from the oven and allow to cool for a while before serving (they also taste great cold). Pour over a little Greek yoghurt and some of the retained strawberry juice. Enjoy!