In a medium, heavy-bottomed saucepan, combine the brown sugar, heavy cream, butter, and salt, if using.

Place the saucepan over medium heat, stirring frequently as the butter melts and the brown sugar dissolves.

Remove the saucepan from the heat and carefully stir in the vanilla extract. The mixture may bubble slightly when the vanilla is added.

Allow the caramel to cool until it is no longer hot. It will continue to thicken as it cools. Set aside approximately 1 cup of caramel for the pie filling and reserve any remaining caramel for decorating and serving.

Preheat the oven to 350°F (175°C).

Add the Biscoff cookies to a food processor and pulse until they are finely crushed and resemble sandy crumbs.

Pour the melted salted butter into the food processor and pulse again until the crumbs are evenly moistened and begin to hold together when pressed.

Transfer the cookie mixture to a 9-inch pie dish. Using the bottom of a measuring cup or your fingers, firmly press the crumbs across the bottom and up the sides of the dish to form an even crust.

Bake the crust for 8–10 minutes, until lightly golden and fragrant.

Remove the crust from the oven and allow it to cool completely before assembling the pie. The crust will continue to firm up as it cools.

In a medium mixing bowl, whisk together the whole eggs, egg yolks, and cornstarch until completely smooth and no lumps remain. Set aside.

In a medium saucepan over medium heat, combine the milk, granulated sugar, salt, and ground cinnamon. Whisk until combined and heat until the mixture is steaming and hot, but not boiling.

Carefully scoop out approximately 1 cup of the hot milk mixture. Slowly drizzle it into the egg mixture while whisking constantly. This process, known as tempering, gradually warms the eggs and prevents them from scrambling.

Slowly pour the tempered egg mixture back into the saucepan with the remaining milk, whisking continuously as you pour.

Continue cooking over medium heat, whisking constantly and scraping the bottom and corners of the saucepan, until the custard begins to thicken and reaches a gentle bubble, approximately 3–5 minutes. Once bubbling, continue whisking and cooking for approximately 1 additional minute to ensure the cornstarch is fully activated.

Remove the saucepan from the heat and stir in the vanilla extract.

Transfer the finished custard to a clean, heat-safe mixing bowl. Press plastic wrap directly onto the surface to prevent a skin from forming.

Allow the custard to cool for approximately 30 minutes, or until it is no longer hot but remains soft and spreadable. Stir briefly if needed before assembling.

Make sure the Biscoff cookie crust has cooled completely and the caramel sauce is no longer hot.

Peel and slice 2–3 medium bananas into approximately ¼-inch-thick slices.

Arrange the banana slices in an even layer across the bottom of the prepared Biscoff cookie crust. Slightly overlap the slices as needed to cover the crust.

Measure approximately 1 cup of the homemade caramel sauce and carefully drizzle it over the banana slices, spreading it gently to create an even caramel layer. Reserve the remaining caramel sauce for decorating and serving.

Spoon the cooled, spreadable vanilla custard over the caramel and banana layers. Gently spread it into an even layer using an offset spatula or the back of a spoon.

Press plastic wrap directly onto the surface of the custard to prevent a skin from forming.

Refrigerate the pie for at least 4–6 hours, preferably overnight, until the custard is completely chilled and firmly set.

When the pie is fully chilled and ready to decorate, place a large mixing bowl and the beaters of an electric mixer in the refrigerator or freezer for approximately 10–15 minutes.

Add the cold heavy whipping cream, powdered sugar, salt, and vanilla extract to the chilled mixing bowl.

Continue whipping until stiff peaks form and the whipped cream holds its shape when the beaters are lifted. Be careful not to overwhip, as the cream can become grainy.

Remove the chilled pie from the refrigerator and carefully remove the plastic wrap.

Slice the remaining 2 bananas and arrange them in an even layer over the chilled vanilla custard.

Spoon the homemade whipped cream over the bananas, spreading it evenly to cover the entire surface of the pie. Alternatively, transfer the whipped cream to a piping bag fitted with a decorative tip and pipe it over the pie.

Drizzle a small amount of the reserved caramel sauce over the whipped cream. Using a spoon, gently swirl the caramel into the whipped cream to create a beautiful marbled appearance.

Crush 1–2 additional Biscoff cookies and sprinkle the crumbs over the top of the pie.

Slice with a sharp knife, wiping the blade clean between cuts for neater slices. Serve chilled with an additional drizzle of homemade caramel sauce, if desired.