Preheat oven to 190 degrees C. Lightly grease a muffin pan, or use patty cups.
In a large bowl, combine sugar, margarine, egg, sour cream and rum essence. Beat together until smooth. In a medium bowl, mix together flour, baking powder, bicarb soda and salt. Blend into egg mixture. Stir in pineapple and coconut. Divide batter into 12 muffin cups.
Bake in preheated oven for 20 to 25 minutes, or until the tops spring back when lightly tapped.