In a bowl, combine water and protein powder and mix.
Set aside for 10 minutes.
Using a beater beat this mixture until foamy.
Add vinegar and beat until combined.
Add icing sugar little at a time and beat to incorporate.
Add xanthan gum and corn syrup and beat. The mix will be extremely thick at this stage.
Add one or two tsp of water and keep beating until the icing comes together.
Add vanilla and beat to incorporate.
You can add more water to use it as flooding while decorating cookies.
The thicker mix can be used for outline.