Add the sugar, flour, dessicated coconut, egg and salt and pulse the food processor until the mixture resembles breadcrumbs (less than a minute)
Add cold water, a tablespoon at a time, until the mixture just begins to come together
Tip the mixture on to the baking tin and press down firmly and evenly especially at the corners & edges (if using a mould, bring the mixture together to form a ball, wrap in cling film and chill for 30 minutes before moulding)
Sprinkle the top with a tablespoonful or so of caster sugar
Cook for 45-50 minutes or until the shortbread just begins to turn golden brown
Slice into fingers/petticoat tails while still warm before allowing to cool on a wire rack