Bring the butter, cream, corn syrup, brown sugar, cocoa powder, and salt to a simmer in a small saucepan. Cook, stirring, until smooth and incorporated.
Remove from the heat, add the chocolate chips and vanilla, and stir until smooth.
Serve warm over ice cream with toppings of your choice - rainbow sprinkles, frosted circus animal crackers, homemade whipped cream - go crazy!
5 minutes | Serves Makes 1 shake (that probably serves 2 people)
1 hour, plus cooling time | Serves 6
4 hours (including freezing) | Serves 6