In a large (no, really, it need to be large!) pot, combine the sugar, buttermilk, butter, corn syrup, baking soda, and salt. Bring the mixture to a boil and boil for 7 minutes, stirring constantly (no, really, stir constantly--this can bubble over in the blink of an eye!).

The mixture will be very bubbly and foamy. As it boils, it will start to develop a deep amber color and smell caramely.

After 7 minutes, remove the mixture from heat. Stir in vanilla extract (it will bubble at first). Serve the syrup warm.

This makes about 2 cups and can be made ahead of time and stored in the fridge. Reheat and give it a good whisk before serving.