Put the tin in the oven and heat for 5 minutes. Mix the flour, baking powder, xanthan gum and salt in a mixing bowl. Add 300ml/10fl oz of the soya milk. Mix well with a large metal whisk until smooth.

Add the soya milk, lemon zest and juice from one lemon. Beat well until the ingredients are thoroughly combined and the mixture is smooth. Quickly spoon the cake mix into the prepared tin ...