Make the Pie Crust:

1. Prepare the Crust:

   • In a medium bowl, combine the flour and salt. Add the cold butter cubes and cut them into the flour using a pastry cutter or your fingers until the mixture resembles coarse crumbs.
   • Gradually add the ice water, 1 tablespoon at a time, mixing with a fork until the dough comes together. You may need a little more water, depending on the consistency of the dough.

2. Chill the Dough:

   • Shape the dough into a ball and wrap it in plastic wrap. Refrigerate for at least 30 minutes.

3. Roll out and Bake the Crust:

   • After chilling, roll out the dough on a floured surface to fit your pie dish. Place the rolled dough into the dish and trim the edges, leaving about an inch of overhang. Fold the edges under and crimp for a decorative finish.
   • Preheat the oven to 375°F (190°C). Line the crust with parchment paper and fill with pie weights or dried beans.
   • Bake the crust for about 15 minutes, then remove the parchment and weights and bake for an additional 10 minutes or until golden brown. Let the crust cool while you prepare the filling.

Make the Butterscotch Filling:

4. Prepare the Butterscotch Base:

   • In a medium saucepan over medium heat, melt the butter. Stir in the brown sugar, flour, and salt until well combined.
   • Gradually whisk in the milk, and bring the mixture to a simmer. Cook, stirring constantly, until the mixture thickens, about 5-7 minutes.

5. Temper the Egg Yolks:

   • In a small bowl, whisk the egg yolks. Slowly add a few tablespoons of the hot butterscotch mixture to the yolks to temper them. Then, gradually whisk the egg mixture back into the saucepan with the butterscotch base.
   • Continue to cook the filling for another 2-3 minutes, until it thickens further. Remove from heat and stir in the vanilla extract.

6. Fill the Pie Crust:

   • Pour the butterscotch filling into the cooled pie crust and smooth the top with a spatula. Allow the pie to cool at room temperature for about 30 minutes, then refrigerate for at least 4 hours to set.

Make the Meringue (optional):

7. Prepare the Meringue:

   • In a clean bowl, beat the egg whites with cream of tartar until soft peaks form. Gradually add the granulated sugar, a tablespoon at a time, until stiff peaks form. Add the vanilla extract and beat for another minute.

8. Top the Pie with Meringue:

   • Spread the meringue over the chilled pie, making sure to seal the edges where the meringue meets the crust.

9. Brown the Meringue:

   • Preheat the oven to 350°F (175°C). Bake the pie for 10-15 minutes, or until the meringue is golden brown. Remove the pie from the oven and let it cool completely.

Serve:

10. Serve and Enjoy:
    • Once the pie has cooled completely, slice and serve. Enjoy the creamy butterscotch goodness topped with golden, fluffy meringue.