1. In a small saucepan set over medium-low heat, melt the butter and unsweetened baking chocolate. Stir until smooth.

  2. Whisk in the half & half.

  3. In a small bowl, whisk together the sugar, cocoa, espresso powder, and salt. Whisk into the butter mixture.

  4. Bring to a boil, then remove from heat and stir in the vanilla. Serve warm.

  5. Store, covered, in the refrigerator for up to 3 weeks.