Melt butter and once cool add to sugar and mix together until creamy.
Add vanilla extract and egg to creamy mixture and beat until fully combined.
Add flour, bicarbonate of soda, baking powder, salt, Xanthan gum and mix well with a wooden spoon.
Add chocolate chips and gently knead into the mixture and then place in the fridge for 30 minutes to firm up.
Line 2 baking sheets with greaseproof paper.
After 30 minutes using an ice cream scoop to scoop the dough onto the lined baking sheet. Leave around 3 inches between cookies. I would not put more than 6 cookies on each baking sheet as you want to allow plenty of room for them to spread.
Place the baking sheet in the fridge for a further 30 minutes.
Preheat the oven to 170°C/325°F/Gas mark 3
Place the baking sheet in the center of the oven and bake for 15 minutes until the edges of the cookies look very lightly golden. Remove from oven and leave to cool on the baking sheet until they are cool and firm before transferring to cooling rack.
I recommend baking the baking sheets of cookies one at a time to ensure they are baked evenly as they are best baked in the middle of the oven.