Stir brown sugar together with 1/4 cup of water in a heavy to medium saucepan over medium to low heat until sugar dissolves. Increase heat, and boil without stirring until syrup is deep amber color, occasionally brushing down sides of pot with wet pastry brush, 2 - 4 minutes. Add butter; stir until melted. Gradually stir in cream. Boil sauce 2 minutes, stirring often. Remove from heat. Add chocolate, Kahlua, and vanilla; stir until chocolate is melted, and sauce is smooth.
Serve over ice cream with grilled bananas, with brownies, brownie cookies, a little whipped cream, or all by itself :)