Preheat the oven to 350 degrees F. Bring a full kettle to the boil for a water bath.
1 cup sugar with a spoonful of water in a heavy-bottomed saucepan
over medium-high heat until the sugar dissolves. Do not stir with a spoon. Swirl the pan slightly over the heat, until the sugar turns golden. Pour the sugar into an 8-inch metal cake pan, swirl to coat the bottom and sides. The sugar will harden in about 5 minutes.
together the coconut milk, eggs
, rum and remaining 1/2 cup sugar. Strain
over the hardened caramel
. Scatter over the lime
zest and toasted coconut, and swirl a bit with a spoon to blend
evenly. Set the cake pan
in a roasting pan and add enough boiling water to come halfway up the cake pan. Bake in the water bath
until set, about 40 minutes. Cool. Refrigerate the flan
at least 4 hours before serving. When ready, dip the bottom of the pan in warm water, place a large plate over the top of the pan, and invert. The flan should unmold
easily with the caramel sauce.