Pre-heat oven to 375 degrees. Line a 9-by-13-inch baking pan with parchment, and grease with butter (I sprayed with baking spray)
Melt 1 stick of butter in a saucepan over low heat.
Add the chocolate wafer cookies to the bowl of a food processor and process to make fine crumbs.
Add the light brown sugar, melted butter and a pinch of salt.
Process until the mixture is the consistency of damp sand.
Dump the mixture into the pan and press it into an even layer.
Bake for 7 to 10 minutes, or until the surface is firm.
Remove the pan from oven and set aside.
Reduce oven heat to 350 degrees.
Brown the butter in a heavy-bottom medium saucepan over medium-low heat.
When the butter has browned (about 3 minutes), set aside to cool.
In a large bowl, whisk together bananas, eggs, dark brown sugar and rum.
Whisk in brown butter.
In a separate bowl, whisk together flour and fine salt.
Pour the mixture over the prepared crust and spread evenly.
Transfer pan to oven and bake until the top is firm and a toothpick inserted in the center emerges with a few crumbs attached; 45 to 55 minutes.
Cool completely on a wire rack; cut into 24 bars.