Preheat oven to 300 F and lightly grease a 9 inch pie pan or springform pan, set aside
Caramelize the sweetened condensed milk by pouring into a small baking dish and covering with foil. Place that small dish into a large roasting pan and fill with enough water to reach about half way up the smaller baking dish. Bake for 1 1/2 hours, or until the toffee is cooked to a toasty, golden brown color. About half way through, check the oven and add more water as needed.
Meanwhile, pulse the biscuits in a food processor until they are crumbs. Mix the crumbs with the softened butter using a fork, then press the mixture into the prepared pan. Chill in the refrigerator until the toffee is done in the oven, and has cooled enough to handle.
Pour about half the toffee over the chilled crust. Slice the bananas, and layer over the first layer toffee then pour the rest of the toffee on top.
Just before serving, whip the heavy cream and sugar on medium to make whipped cream, then spoon it over the top of the pie.