Microwave version: In a large microwave safe bowl, add the butter, sugar, and corn syrup. Microwave for 5 minutes stirring halfway. Remove and stir well. Microwave for 2 more minutes. Remove from heat and add the vanilla and baking soda.
Stovetop version: In a large saucepan, bring the butter, sugar, and corn syrup to a boil then start the timer and cook for 4 1/2 minutes at a boil. Remove from the heat and stir in the baking soda and vanilla.