In a saucepot over medium heat, stir together the sugar, butter, milk, and salt. As it melts, whisk to combine it into a smooth sauce.
Allow the sauce to bubble gently for about 5 minutes.
When the sauce is smooth and has thickened, but is still pourable, remove it from the heat.
Stir the vanilla extract into the sauce.
Serve the sauce while warm and pourable over your favorite dessert, such as vegan chocolate cake. Store any leftover sauce in a sealed jar in the fridge. Reheat it slightly to serve again.