Add sugar, flour and salt into a medium saucepan and mix.
Add in the almond milk and vanilla extract.
Turn on the heat to medium and stir until the mixture starts to boil
Keep stirring continuously for the next 2 minutes until the mixture thickens to a pudding-like texture. After this, remove the pan from the heat
Transfer to a bowl, wrap it with a plastic wrap and let it cool down to room temperature. The plastic wrap ensures that the mix does not create a dry thin layer on top.
On a separate bowl, beat up the butter to a fluff using an electric beater.
Add the flour mix to the butter, 1 tbsp at a time and beat until mixed well. Repeat this till all the flour mix is added in.
The frosting is ready at this point. You can store it in the fridge in an airtight container for up to one week (Let it reach room temperature and whip it up before using)