Prepare brownie mix according to package directions, stirring in mashed bananas just before transferring mixture to a 9-inch square pan. Bake according to package directions.
Meanwhile, stir together sugar, next 3 ingredients, and 1 1/4 cups heavy cream in a medium saucepan. Cook over low heat, stirring often, 35 to 45 minutes or until dark amber. Stir in 1 cup heavy cream, and increase heat to medium. Cook, stirring constantly, about 5 minutes or until slightly thickened. Remove from heat, and cool 5 minutes.
Cut cooled banana brownies into 3/4-inch cubes. Layer brownie cubes and desired amount of sticky toffee sauce in each of 12 small jars or bowls. Beat remaining 1 1/4 cups heavy cream at high speed with an electric mixer until soft peaks form; spoon over puddings. Drizzle with more sauce, if desired.
Note: Refrigerate cooled sauce in an airtight container up to 3 days. To soften, microwave at 30 second intervals, stirring until soft.