01 -
Ensure the pie crust is fully baked and cooled before filling.
02 -
In a medium saucepan, whisk together the brown sugar, flour, and salt until well blended.
03 -
Gradually whisk in the milk to create a smooth mixture with no lumps.
04 -
Set the saucepan over medium heat and cook, stirring constantly, until the mixture thickens and begins to bubble, about 7–10 minutes.
05 -
Slowly whisk a little of the hot mixture into the beaten egg yolks to temper, then pour the yolk mixture back into the saucepan, stirring continuously.
06 -
Continue to cook the filling for an additional 2–3 minutes over medium heat, stirring constantly, then remove from the heat.
07 -
Stir in the butter and vanilla extract until the filling is smooth and glossy.
08 -
Pour the hot butterscotch filling into the cooled pie crust and smooth the surface with a spatula.
09 -
Refrigerate for at least 2 hours, or until the filling is completely set.
10 -
Top with whipped cream or meringue. Garnish with butterscotch chips or grated chocolate before serving.