In a small saucepan, heat the butter just until melted. Add the brown sugar and salt. Mix to combine over medium heat. When the sugar starts to melt and the mixture no longer resembles wet sand, add the heavy cream.

Whisk the mixture until combined. Bring to a boil, stirring occasionally to prevent the bottom from burning. Let it boil for 10 minutes until it thickens slightly. Take it off the heat and add the vanilla extract. Let it cool to room temperature. Cover with plastic wrap to prevent a layer forming on top.

For each cup, I add two tablespoons of butterscotch and 5oz of cream soda. You can adjust the flavor by adding more butterscotch. Mix to combine. Serve in chilled glasses.