Make the caramel sauce: Combine brown sugar, half & half, and salt in a saucepan over medium-low heat. Add the butter and stir with a whisk until it reaches a boil. Keep stirring and allow to keep cooking until it thickens, about 5 minutes. Remove from heat and cool slightly, then pour into an airtight container and store in the fridge for up to 2 weeks.

Fill 2 glasses with ice, then pour cold-brew coffee over. Add half & half, then drizzle caramel sauce over top. Drink!