
Line an 8-inch square baking pan with parchment paper.
In a medium saucepan, combine the sugar, heavy cream, and whole milk. Place over medium heat and cook, stirring occasionally, until the sugar dissolves.
Increase the heat to medium-high and bring the mixture to a boil. Use a candy thermometer to monitor the temperature.
Reduce the heat to medium-low and simmer until the mixture reaches 235°F (118°C), the soft-ball stage.
Remove the saucepan from the heat and stir in the chocolate chips until they are melted and the mixture is smooth.
Stir in the vanilla extract, coffee powder, and sea salt.
Pour the mixture into the prepared baking pan and smooth the top.
Drizzle the caramel sauce over the top of the fudge.
Let the fudge cool to room temperature, then refrigerate until set, about 2 hours.
Cut into squares and serve.