Prepare the Crust:Preheat oven to 325°F (163°C). Grease a 9-inch deep-dish pie pan with nonstick spray.In a bowl, combine graham cracker crumbs, sugar, and salt. Add melted butter and stir until the mixture resembles wet sand.Press the mixture evenly into the bottom and up the sides of the prepared pie pan.Bake for 6–8 minutes, then set aside to cool completely.
Make the Toffee Filling:In a large saucepan, melt the butter over medium-low heat. Add brown sugar and cook, stirring constantly, until the sugar dissolves, about 5 minutes.Stir in sweetened condensed milk and heavy cream. Increase heat to medium and bring to a boil. Boil for 5–10 minutes, stirring constantly, until the mixture reaches 220°F (104°C).Remove from heat and stir in vanilla extract. Pour the toffee into the cooled crust and refrigerate for 2–3 hours, or until firm.
Assemble the Pie:Once the toffee layer is firm, arrange the banana slices in two layers over the toffee.In a mixing bowl, whip the heavy cream, powdered sugar, and vanilla extract on high speed until stiff peaks form.Spread the whipped cream over the bananas, ensuring it covers them completely to prevent browning.Garnish with chocolate shavings or toffee bits, if desired.
Serve:Serve the pie immediately or refrigerate until ready to serve. Best enjoyed within 1–2 days.