Preheat oven to 350°F.
In a medium bowl, stir together graham cracker crumbs, melted butter, brown sugar, and salt.
Firmly press mixture into the bottom and up the sides of a 9-inch deep-dish pie plate.
Bake until lightly set, about 8 minutes. Set aside.
Pour 1½ cups dulce de leche into bottom of crust.
Top with bananas, arranging in concentric circles, overlapping slightly.
Sprinkle with ½ cup toffee bits; drizzle with ¼ cup dulce de leche.
Using a stand mixer or hand mixer, beat cream and 3 Tbsp. sugar at medium high speed until soft peaks form. Stir in vanilla.
Spoon whipped cream over banana layer.
Drop teaspoons of dulce de leche over whipped cream layer; swirl using the back of a spoon.
Refrigerate 30 minutes to 3 hours.
Garnish with toffee bits and banana slices.