- Melt butter in a small saucepan over medium heat. Once the butter has completely melted, add the sugar, heavy cream, espresso powder, and salt and whisk until all of the espresso powder has dissolved. Bring the mixture to a slow boil, whisking constantly during this time. Turn down the heat to low, and simmer and whisk for an additional 3 minutes to thicken.
- Remove caramel sauce from the heat and add the vanilla extract. Stir to combine. Serve warm, at room temperature, or pour into a glass jar and refrigerate for later use. The caramel sauce will thicken once it cools. The sauce will keep refrigerated for 2 to 3 weeks.
- To rewarm, microwave on low power in bursts of 10 to 20 seconds, stirring between each session. Or reheat gently over low heat in a saucepan.