Preheat your oven to 350°F (177°C). In a food processor, crush 32 Biscoff cookies until finely ground. Transfer to a mixing bowl, stir in 6 tablespoons of melted unsalted butter, and press firmly into the bottom and sides of a 9-inch pie dish. Bake for 10-12 minutes until golden brown, then cool completely.

In a medium bowl, whisk together 6 beaten egg yolks until smooth. In a saucepan over medium heat, combine 3/4 cup granulated sugar and 1/4 cup water. Cook, stirring until the mixture turns a deep golden caramel color, about 5-7 minutes. Carefully stir in 1/4 cup heavy cream until smooth.

In another saucepan, whisk together 1/3 cup cornstarch, 1/2 cup packed brown sugar, and 3/4 teaspoon salt. Gradually add in 3 cups of whole milk, whisking constantly over medium heat until it reaches a boil and thickens slightly in about 5-7 minutes. Remove from heat and slowly pour in the caramel mixture. Temper the egg yolks by whisking the hot milk mixture into them gradually.

Return the combined mixture to the stove and cook over medium heat, stirring constantly for 2-3 minutes until thickened to a pudding-like consistency. Remove from heat and stir in 1 tablespoon of unsalted butter and 1/2 teaspoon of vanilla bean paste until fully incorporated.

Pour the warm butterscotch filling into your cooled Biscoff cookie crust, smooth the top with a spatula. Allow the pie to cool at room temperature for 30 minutes, then cover and refrigerate for at least 6 hours or overnight for best results.

Just before serving, whip 1 1/2 cups of heavy whipping cream with an electric mixer until soft peaks form. Gradually add 2 tablespoons of powdered sugar and 1/2 teaspoon of vanilla bean paste, continuing to whip until stiff peaks form.

Spread the whipped cream generously over the chilled pie. Optionally, sprinkle crushed Biscoff cookies or finely chopped pecans on top. Serve chilled.