Using either a hand mixer or a stand mixer equipped with a whisk attachment, beat the heavy cream, sugar, and vanilla extract on medium-high speed. Continue whipping until medium peaks form, typically around 3-4 minutes. Medium peaks are firm but still have a slight softness, making them ideal for spreading or piping on desserts.
Spread a layer of dulce de leche over the cooled crust. Arrange the banana slices in one or two layers on top of the dulce de leche. Finally, generously spread the whipped cream over the banana slices.
Refrigerate the pie, uncovered, for at least 2 hours or up to 24 hours. Before serving, garnish with your choice of chocolate shavings, chopped nuts, or toffee bits if desired.
Store any leftover pie in the refrigerator, covered, for up to 5 days.