Preheat the oven to 170°C/225°F/Gas Mark 3. Grease the sides and line the bottom of the baking tins with parchment paper.
In a large bowl mix together flour, sugar, baking powder, baking soda, cocoa powder, xanthan gum, and salt.
In a separate bowl combine the eggs, milk, melted butter, and hot water. Mix well.
Add the wet ingredients into the larger bowl that contains the dry ingredient mix and whisk until fully combined and resembles a smooth chocolate cake batter.
Divide the chocolate cake batter between the 3 baking tins. Place in the oven and bake for approximately 20-25 minutes. Insert a skewer into a cake. If it comes out clean it's ready if not leave it in slightly longer. (Times may vary slightly depending on the oven).
You can divide between two tins if you would rather at 2 layer cake. Baking time will be slightly longer.
Transfer to a cooling rack. Carefully remove from the tins once slightly cooled as the cake will be delicate to handle.