Preheat your oven to 180°C and line a standard loaf tin.
Make the cake batter by whisking butter and caster sugar in a large bowl until creamy. Add the eggs 1 at a time and continue to whisk until fully combined. Add the orange extract and dairy free milk and whisk again.
In a separate bowl mix self raising flour, xanthan gum, baking powder and cocoa powder. Add the dry ingredients to the wet ingredients and mix well.
Transfer the mixture to the lined baking tin and bake in the oven for 45-50 minutes, until a skewer comes out clean. Leave to cool in the tin before making your buttercream.
Make your buttercream by beating butter with an electric whisk until creamy. Slowly add your icing sugar and cocoa powder, continuing to whisk until creamy and combined (this can take around 5 minutes). Whisk in the orange extract and dairy free milk.
Spread (or pipe for a neater cake) the buttercream on top of the cake and decorate with the grated zest of an orange and the dairy free chocolate orange segments. Store in an airtight container for up to 4 days.