Combine the brown sugar, corn syrup, butter and salt in a heavy bottomed saucepan. Bring to a boil and then boil for 5 minutes without stirring. Remove from the heat and mix in the baking soda and vanilla, stirring well.
1 cup brown sugar, 1/2 cup corn syrup, 1/2 cup butter, 1/2 teaspoon salt, 1/2 teaspoon baking soda, 1 1/2 teaspoon vanilla extract