Preheat oven to 350 degrees. Line an 8×8 glass dish with parchment paper and lightly spray with nonstick cooking spray. Set aside. In large bowl, combine butter, sugar, flour and vanilla until dough forms. Press evenly into the bottom of prepared dish. Bake 10 minutes.
Remove from oven and gently pour sweetened condensed milk evenly over hot cookie base. Reduce oven temperature to 325 and bake 15-17 minutes more until milk darkens and turns into toffee.
Remove from oven and cool to room temperature. Using the foil or parchment, lift bars out of glass dish. Slice bananas and place over top of toffee. Spread whipped cream over top of bananas. Slice and refrigerate. When ready to serve, drizzle caramel sauce over top.