Place egg whites into the Thermomix bowl and whip 2 min/37°C/Butterfly/speed 3/MC off. Remove Butterfly.
Add 400 grams of the sugar and whip 1 min/speed 4. Insert Butterfly and whip 1 min/Butterfly/speed 3. Add remaining icing sugar if needed.
To use as 'cement' for any cakery, scrape out of the Thermomix bowl and place into a bowl, cover with a very wet tea towel, almost touching the surface of the icing with the cloth. Use in small amounts as required.