Prepare the Pie Crust: In a large bowl, combine flour and salt. Cut in the cold butter until the mixture resembles coarse crumbs. Gradually add ice water until the dough holds together. Wrap in plastic and chill for 30 minutes. Roll out the dough, fit it into a 9-inch pie pan, and bake at 375°F (190°C) for 12-15 minutes or until lightly golden brown.
Prepare the Butterscotch Filling: Melt the butter over medium heat, add brown sugar and cook until dissolved. Gradually add milk while stirring. In another bowl, whisk egg yolks and cornstarch, then pour in the hot sugar mixture while whisking. Return to the saucepan, cook until thickened, then stir in vanilla extract and salt.
Assemble and Chill the Pie: Pour the butterscotch filling into the pre-baked pie crust. Cool at room temperature for 30 minutes, then refrigerate for at least 4 hours or overnight.
Add Topping and Serve: Top with whipped cream or meringue if desired. Slice and enjoy!
Notes
Stir constantly while cooking to prevent burning and use quality brown sugar for a richer flavor.