Preheat the oven to gas 4 / 180C / 350F and line a 12 hole cupcake tin / muffin with paper cases
Mix the flour, xanthan gum if using, baking powder and bicarb together
Cream together the sugar and margarine
Put the pineapple chunks, juice, coconut milk, lemon juice and rum essence in a blender and puree
Add it to the creamed margarine & sugar. The mixture will look curdled. Don't worry!
Add into the flour mixture gradually as to avoid the batter clumping
Once it's all mixed in, divide equally between the paper cases
Bake for 25 - 30 minutes or until firm and risen. FYI if you use a muffin tin rather than a cupcake tray they will appear taller and not as spread out
Let cool in the tin for 10 minutes then remove the cakes to a wire rack to cool completely
Meanwhile, make the buttercream. Cream together the icing sugar and margarine until light
Add the coconut milk and vanilla extract to loosen to a piping consistency and ice the cakes
Sprinkle the desiccated coconut over the buttercream
Add a cherry and a pineapple chunk on top with a trimmed cocktail umbrella for garnish
