Mocha Filling

Directions

1. 1
   Prepare an ice-water bath; set aside.
2. 2
   In a large heatproof bowl set over a pan of simmering water, combine the sugar, cornstarch, and salt.
3. 3
   Add the chocolate, half-and-half, egg yolks, and egg; whisk until the chocolate is melted, about 3 minutes.
4. 4
   Slowly add the coffee, whisking constantly.
5. 5
   Cook, stirring with a wooden spoon, until the mixture is thick enough to coat the back of the spoon, 2 to 3 minutes.
6. 6
   Remove from heat; stir in the butter.
7. 7
   Place the bowl in the ice bath; stir occasionally until the mixture is cool.
8. 8
   Store in an airtight container at room temperature up to 1 day.