Magelby's Buttermilk Syrup

1 cube butter
1 cup sugar
1 cup buttermilk
1 Tbsp vanilla
1 Tbsp corn syrup
1/2 tsp baking soda

Bring first five ingredients to a boil. Add baking soda. Boil 10 seconds and remove from heat immediately to avoid boil over. Use a fairly deep, heavy pan.