Preheat oven to 350°F. Brush a 1 1/2- 2 quart baking dish with 1 Tbsp melted butter. Set aside.
To make bananas: On the stove top using a large 12 inch skillet, melt reserved 4 Tbsp butter with heavy cream, corn syrup and brown sugar over medium-high heat. Heat stirring, just until sugar has dissolved. Remove from heat, add rum and vanilla. Mix well. Add bananas, tossing until coated. Pour into prepared baking dish. (The skillet should be big enough to double as a mixing bowl)
To make the topping: In a medium-size mixing bowl, toss together oats, brown sugar, flour, cinnamon and salt.
Use a pastry blender to cut cold butter into dry ingredients until it resembles cornmeal. Add walnuts, toss to evenly distribute. Sprinkle evenly over bananas.
Place into oven baking for 30-40 minutes or until golden and bubbly.
Let stand for 5 minutes then serve with a big scoop of vanilla ice cream.
Notes
Please note:
When using an oven safe skillet, you may opt to prepare the bananas on the stovetop then bake the bananas foster crisp in the same skillet instead of transferring to a baking dish.
When doing so you'll be starting with a hot skillet so the bake time may be less, adjust accordingly.