Preheat the oven to 325°F(165C°). Grease 8 inch (20cm) square oven-proof dish and line the bottom and sides with parchment paper, about 2 inches(5 cm) of overhang on each side.
Dough: Put the sugar and lemon zest in a big bowl and mix with a fork or rub with your fingers to increase the lemon flavor. Add in the flour and mix well. Add the cubed butter and rub them with your fingers or use a fork until the mixture resembles crumbs. Add in the lemon juice and stir with a spatula. Transfer the dough into the square dish and spread it evenly with your fingers or with a spoon. Bake for almost 30 minutes until the edges are brown and the top is lightly brown. Let the crust cool in the dish on a wire rack.
White Chocolate Ganache: While the crust is cooling, start to make the ganache. Place the white callets/roughly chopped white chocolate in a medium heat-proof bowl and set aside. Put the heavy cream in a small pan and place it over med-low heat. When the heavy cream scalds-small bubbles appear at the sides of the pan, take the pan from the heat and pour onto white chocolate. Let the cream soften and melt the chocolate for 20 seconds without stirring. Gently stir the mixture with a spatula until no chocolate pieces remain and become a smooth ganache. (If there are some white chocolate pieces in your ganache, place it in the turned off oven- that is still warm as you just baked the crust-for almost 1-3 minutes depending on the unmelted chocolate pieces. Remove from the oven and stir until you have a smooth ganache.)
Assemble: When the crust and ganache are cooled(it takes almost 1 hour in total-crust will be cool in 1 hour and ganache will be cool enough in almost 20 minutes while crust is cooling), pour the ganache over the dough. Then cover the top with desiccated coconut. Let it cool for 1 hour at room temperature. Then keep the dish in the freezer for almost 1 hour until the ganache sets. Alternatively, you can keep in the fridge for longer. Make sure the dish is totally cool before you place it in the freezer or in the fridge. Remove the dish from the freezer. Lift the parchment paper from the sides to remove the uncut bars from the dish. Cut them into 16 squares and enjoy! You can keep in the fridge for almost 4 days.