In a medium mixing bowl, whisk together (or use an electric mixer) sugar, dry milk, and hot water until no clumps remain, approximately 2½ minutes, and sugar and milk have dissolved. It should be smooth.
Allow to rest and thicken for 10 minutes.
Use immediately or store in a sealed container in the fridge for 4-6 days.
Notes
To combine ingredients faster, an electric mixer can be used.
Refrigerate in a sealed container for up to 4-6 days.