Preheat the oven to 350°F (180°C).

In a food processor, pulse the Speculoos cookies until finely ground. Add the melted butter and pulse until moistened. Press the mixture into a 9-inch pie plate, covering the bottom and sides. Bake for about 12 minutes until fragrant. Let it cool on a wire rack.

Whisk the egg yolks in a large heatproof bowl until smooth.

In a saucepan, combine the granulated sugar and water. Cook over medium heat until the sugar dissolves. Increase the heat to medium-high and cook until it turns dark amber, about 10 minutes. Remove from heat and gradually stir in the heavy cream, being careful as it will bubble up.

In another saucepan, mix the brown sugar, cornstarch, salt, and half of the milk. Whisk in the remaining milk. Bring to a boil over medium-high heat, whisking often to prevent sticking. Remove from heat and add the butterscotch mixture, stirring well.

Gradually add a quarter of the hot liquid to the egg yolks, whisking constantly to temper the eggs. Return the mixture to the saucepan and bring to a boil. Cook for 2-3 minutes until thickened, stirring continuously. Remove from heat, stir in the butter, and strain into the prepared crust. Chill for at least 6 hours.

In a mixing bowl, beat the cold cream until it thickens. Add the powdered sugar and vanilla, and beat until soft peaks form. This will create a luscious topping for your pie.

Spread the whipped cream over the chilled pie. Sprinkle crushed Speculoos cookies on top if desired for an extra crunch. Serve chilled and enjoy!