Preheat oven to 180 degrees celsius (fan-forced). Line 2 large baking trays with baking paper and set aside.
Place the caster sugar, butter and grated lemon zest into the Thermomix bowl and mix for 10 seconds, Speed 4. Scrape down the sides of the bowl and repeat 2-3 more times, or until pale and creamy.
With the blades turning on Speed 4, add the eggs one by one through the MC hole.
Add the self-raising flour and desiccated coconut and mix for 5 seconds, Speed 5. Scrape down the sides of the bowl and repeat until well combined.
Place tablespoonfuls of the mixture onto the prepared baking trays (leaving a 4-5 cm gap between each biscuit to allow for spreading) - see notes.
Bake for 15 minutes or until lightly golden. Allow to cool for 10 minutes on the baking trays before transferring to a wire rack to cool completely.
Meanwhile, to make the glaze, place the icing sugar, lemon juice, lemon zest and butter into a clean Thermomix bowl. Mix for 10 seconds, Speed 4.
Melt for 1 minute, 80 degrees, Speed 2.
Place the lemon icing into the fridge to firm up slightly.
Spread the glaze over the completely cooled biscuits and sprinkle over extra desiccated coconut and grated lemon zest.
Store in an airtight container at room temperature for up to 1 week (or freeze for up to 1 month).