Place the warm water in a jug (it should be around skin-temperature) and stir in the caster sugar until dissolved. Add the yeast, stir and then cover with a tea towel and leave in a warm spot for 7-10 minutes. It should form a head like on beer - when it does it's ready to use.

Add the gluten free flour, xanthan gum and 1 tsp salt to a large mixing bowl and stir.

When the yeast mixture is ready, form a well in the centre of the flour mix and pour in. Mix together with a wooden spoon until it forms a thick batter.

Add 3 tbsp olive oil to the mixture and fold in with the wooden spoon until mixed well.

Use 1 tbsp olive oil to generously grease a 20cm-diameter round tin. Pour the bread mixture in and use oiled fingers to spread it out evenly in a flat layer. Cover loosely with oiled clingfilm and place in a warm, draft-free spot for around an hour to prove.

Once the dough has proved, it should have expanded in size. Heat the oven to 220'C / Fan 200'C / Gas Mark 8. Use an oiled thumb or finger to poke dimples into the top of the focaccia dough and press sprigs of rosemary into these at random.

Drizzle with extra oil (around 1 tbsp) and bake in the oven for 20-25 minutes. The focaccia should be golden and crisp on top and sound hollow when tapped.

Remove from the oven and sprinkle with the sea salt flakes. Allow to cool for 10-15 minutes before turning out of the tin and slicing up to serve.