Step 1: Prepare the Pie Crust

1. Bake your pie crust according to package or recipe directions.
2. Let it cool completely before filling.

Step 2: Make the Butterscotch Filling

1. In a medium saucepan, whisk together brown sugar, cornstarch, and salt.
2. Gradually whisk in the milk until smooth.
3. Place over medium heat and cook, stirring constantly, until the mixture thickens and begins to bubble (about 6-8 minutes).
4. Remove from heat. Temper the egg yolks by adding a spoonful of hot mixture into the yolks while stirring.
5. Slowly whisk the tempered yolks back into the saucepan.
6. Return to medium heat and cook for another 2-3 minutes, stirring constantly.
7. Remove from heat and stir in butter and vanilla until smooth.

Step 3: Fill and Chill

1. Pour the warm filling into the cooled pie crust.
2. Smooth the top with a spatula.
3. Let cool at room temperature for 20-30 minutes.
4. Refrigerate for at least 4 hours or until fully set.