Pour condensed milk into an 8 inch glass pie plate. Cover with foil
Fill a shalllow 2-quart casserole dish with 1/4 inch hot water. Place covered pie plate in casserole dish and bake at 375 degrees for 45 minutes or until condensed milk is thick and caramel colored, adding hot water to water bath as necessary,
Cut bananas crosswide into 1/8 inch thick slices and place in bottom of pie crust. Spread caramelized milk over bananas. Cool for 30 minutes.
Combine whipping cream and sugar; beat until very stiff. Spread over caramelized bananas and sprinkle with crumbled heath bars. Chill 3 hours or overnight before serving.