For the Hot Fudge Sauce: Heat a medium-sized, heavy-bottomed saucepan over medium-high heat then add the chocolate, heavy cream, corn syrup, brown sugar, cocoa powder, and salt. Bring to a bubble while stirring constantly then turn heat down to medium-low and simmer while stirring for 5 minutes.
Remove pan from heat then add butter and vanilla and stir until smooth and melted. Let hot fudge sauce cool until warm then transfer to a container or jar with a tight fitting lid. Can be made ahead of time. To reheat, microwave in 20 second increments, stirring between increments, until warm.
Scoop ice cream into dishes then drizzle with Hot Fudge Sauce and peanuts and then serve.