Step 1: Prepare the Crust. In a medium bowl, combine graham cracker crumbs and granulated sugar. Pour in the melted butter and mix until well combined. Press the mixture firmly into a 9-inch pie plate, extending up the sides. Bake at 350°F (175°C) for 8-10 minutes, then let cool completely on a wire rack.
Step 2: Make the Butterscotch Filling. In a medium saucepan, melt ½ cup butter over medium heat. Whisk in the brown sugar, flour, and salt. Cook, stirring constantly, for 2-3 minutes until a thick paste forms. Gradually whisk in the whole milk until smooth. Bring the mixture to a gentle boil, then reduce heat and simmer for 1 minute, stirring.
Step 3: Thicken the Filling. In a small bowl, whisk the beaten egg yolks. Slowly temper the egg yolks by gradually whisking about ½ cup of the hot butterscotch mixture into them. Then, pour the tempered egg yolk mixture back into the saucepan with the remaining butterscotch mixture. Cook over medium-low heat, stirring constantly, for another 2-3 minutes until the filling thickens. Do not boil.
Step 4: Finish and Chill. Remove the filling from heat and stir in the vanilla extract. Pour the butterscotch filling into the cooled graham cracker crust. Cover the pie with plastic wrap, pressing it directly onto the surface of the filling to prevent a skin from forming. Chill in the refrigerator for at least 4 hours, or until completely set.
Step 5: Prepare Whipped Cream Topping. In a large mixing bowl, beat the heavy whipping cream, powdered sugar, and vanilla extract with an electric mixer on high speed until stiff peaks form.
Step 6: Serve. Once the pie is fully chilled, remove the plastic wrap. Spoon or pipe the whipped cream over the top of the pie. Garnish with chopped toasted pecans, if desired. Slice and serve immediately. Enjoy your Butterscotch Heaven Pie!