2) Add the egg and beat until well combined, approximately 1 minute. Turn off the mixer and add 100g of the sugar. Mix on low until combined. Stop to scrape down the sides of the bowl. Repeat until all of the sugar has been incorporated.
3) Add the vanilla and continue to beat until the icing is smooth and light, approximately 2 to 3 minutes.
4) Use immediately or store in an airtight container at room temperature for up to 4 hours or refrigerate for up to a week. Bring to room temperature before using.