Line a 9-inch pie pan with:
Bake or chill the crust as directed in the recipe, About Crumb Crusts or About Blind Baking Crusts.
Combine in a medium heavy saucepan and cook over medium heat, stirring, until melted and bubbling, 3 to 5 minutes:
Remove from the heat and gradually stir in:
If necessary, return briefly to the heat to melt the butterscotch. Let cool slightly. Whisk in a separate medium heavy saucepan until well blended:
Gradually whisk in:
Whisk in the butterscotch. Whisk in until no yellow streaks remain:
Stirring constantly with a silicone spatula, bring to a sputtering simmer over medium heat. Simmer for 1 minute, scraping the corners of the pan well. Off the heat, stir in:
Spoon the filling into the crust and press a sheet of plastic wrap directly on the surface. Refrigerate the pie for at least 3 hours to firm the filling. Shortly before serving, remove the plastic wrap and cover the pie with: