In a medium sized saucepan over medium heat, melt the butter. Add the brown sugar and stir frequently, until it is all melted and bubbling vigorously. This can take 3 to 5 minutes. It will brown faster on the edges, so be sure to stir.
Remove from the heat and slowly whisk in the heavy cream. It may splatter. If the brown sugar turns hard when adding the cream, return to the heat and simmer for a couple of minutes. Whisk in the milk, vanilla bean, and salt.
In a small bowl, whisk together the cornstarch and eggs until the cornstarch dissolves. Whisk 1/4 cup of the hot cream mixture into the egg mixture, so it is warm. Whisk the cornstarch mixture back into the pot of butterscotch cream mixture.
Cook over medium heat, whisking constantly, until the pudding comes to a boil. Continue cooking and whisking for 2 more minutes (add the whiskey now, if using!). The pudding will become thick and should be boiling while you whisk. Don’t skimp on the 2 minutes or your pudding will not set up properly.
If there are any lumps, strain the pudding through a strainer into a large measuring cup or anything that will pour cleanly. Divide pudding into small cups, glasses or bowls, cover, and chill. You can eat it warm as well! Top with creme fraiche or lightly whipped cream and the caramelized bananas (recipe below).