Combine buttermilk, sugar, butter,corn syrup, and baking soda in a large pot. Like one you'd make soup in. Yes, you'll have way more pot than ingredients (and I'm not referring to the green leafy stuff), but this will boil all over your newly-cleaned stove if you put it in a smaller saucepan.
Bring ingredients to a boil and reduce heat to low (as long as it's still bubbling, you're okay). Cook, stirring very frequently, for 8-9 minutes. You're basically making candy here and candy-making requires constant vigilance. When it's done, it should take on this luscious golden-brown color. Remove from heat and add vanilla. There will be foam on top. It tastes just as good, but it's not super pretty. If you're into aesthetics, you can skim it off; otherwise, just give it a good stir.