Thaw unbaked pie crust and roll onto a 9-inch pie pan. Bake in pie pan according to pie crust instructions, until golden brown. Set aside while preparing the pie filling.
In a small bowl, lightly beat your egg yolks and set aside.
In a medium saucepan over medium-high heat, combine brown sugar, flour, cornstarch, salt and cinnamon with the two cups of milk. Whisk together and cook until thickened (it should be a thick consistency so could take up to 10-15 minutes depending on heat level, but this can vary, so be sure it is thick before going to the next step).
Temper eggs by adding a spoonful of hot mixture to the egg yolks. Gradually whisk In egg yolks to saucepan and stir well.
Stir in butter and vanilla extract. Cook, whisking regularly, for another 5 minutes. Mixture should thicken up again.
Pour pie filling Into prepared pie pan and allow to cool for at least 30 minutes before refrigerating for at least 2 hours (preferably overnight) until ready to serve.
When ready to serve, garnish with a dollop of whipped cream and a dash of cinnamon to pie and enjoy!
Notes
If you want to add butterscotch chips, add them in along with the butter and vanilla extract. Stir until melted and pour into baked pie crust.