Preheat oven to 350 degrees F. Lightly grease a 9" round pie plate with cooking spray and set aside. Meanwhile, in a medium bowl, combine your Biscoff cookie crumbs and the melted butter until moistened and mixture resembles wet sand. Press the mixture into and up the sides of the pie plate in an even layer. I do this with my fingers and the flat bottom of a measuring cup or glass. Bake the crust for 12 minutes, then remove from the oven.

While crust bakes, make your filling! Melt the butter in a medium saucepan over medium heat. Remove from the heat briefly to whisk in the flour until it becomes a smooth paste (called a roux). Add in the brown sugar and stir to combine, then return to the heat and add in the milk and salt. Cook, stirring constantly, over medium-high heat until mixture thickens, about 5-10 minutes. Reduce the heat and continue cooking 1-2 minutes more. Remove from the heat.

Working quickly and carefully, pour a little of the pudding into a small bowl with the beaten egg yolks and whisk it vigorously to temper the egg yolks and bring them to temperature. This will ensure you won't have scrambled eggs in your pudding! Once the egg mixture is combined and smooth, add the egg mixture back to the original pot with the remainder of the pudding and turn the heat back onto medium-high. Bring to a boil and whisk constantly for 2 more minutes. Remove from the heat a final time and whisk in your vanilla extract.

Pour the hot pudding mixture into the baked crust and smooth out the top. Allow pie to cool off some before covering it with plastic wrap and refrigerating it. I highly recommend refrigerating it for at LEAST 6 hours, preferably overnight, before serving so it has ample time to chill and set.

Just before serving, top with fresh whipped cream and a sprinkling of crushed Biscoff cookies, if desired.