Prepare the Vegan Buttermilk by combining dairy-free milk with apple cider vinegar. Let sit for 5-10 minutes until it curdles.

Mix dry ingredients: Self-raising flour, baking powder, caster sugar, and bicarbonate of soda until blended.

Combine all ingredients: Add the vegan buttermilk, sunflower oil, vanilla extract, and mango purée to the dry mixture.

Preheat oven to 180°C (350°F) and bake the sponge cakes for 25-30 minutes until a toothpick comes out clean.

Make the buttercream by creaming dairy-free butter and gradually adding powdered sugar and mango purée until smooth.

Assemble the cake by layering sponges with buttercream, mango purée, and desiccated coconut between each layer.

Decorate the cake with remaining buttercream, desiccated coconut, and garnish with mango slices and rosemary.