Pre-heat the oven to 200ºC.
Line a large baking sheet with baking paper.
Sift the flour and bicarbonate or soda into a bowl.
Rub in the butter until mixture resembles breadcrumbs.
Add the sugar and dessicated coconut and mix well.
Use your hands to form a dough.
Divide mixture into 3 equal portions.
Take one portion and squeeze into a long sausage shape and place on baking paper.
Use your hands to shape into a long rectangle about 5.5 cm by 27 cm.
Then repeat with the other 2 portions and space apart well on baking sheet as they will spread.
Bake on middle shelf of oven for 10 minutes (or until golden).
Make up the glaze by mixing the icing sugar with the rum and water.
When the cookies are ready and whilst still warm, spoon the glaze down the middle of each length and then make diagonal cuts.
Transfer to a cooling rack.
Store in an air tight container.