• Preheat the oven to 400º. Line a pie crust with parchment paper and add pie weights or dried beans. Bake for 15 minutes. Remove the pie weights and bake an additional 15 minutes until golden brown. Allow to cool. Turn the oven down to 350º.
• In a medium saucepan, whisk the brown sugar, flour, and salt together. Slowly whisk in the milk. Place over medium heat and cook, whisking constantly until thick and bubbly, about 3-5 minutes. Reduce to low and continue to cook for 2 minutes. Remove the pan from the heat.
• Separate the eggs, reserving the whites for the meringue. Place the yolks in a measuring cup or glass bowl and beat with a fork. Add about a half of a cup of the hot milk mixture a tablespoon at a time to the egg yolk until it is warm. Then slowly add the egg mixture to the milk mixture in the saucepan, whisking until incorporated, Return to low heat and cook for another 2 minutes until it is creamy and smooth. Remove from the heat and add butter and 2 teaspoons of vanilla. Pour into the cooled pie crust.

Meringue

• Beat the egg whites with an electric mixer on high for 1-2 minutes until soft peaks form. Add cream of tartar and ½ teaspoon vanilla, mix to combine. With the mixer on high, slowly add the sugar and beat until stiff peaks form and it is shiny, about 2 minutes.
• Spoon the meringue over the pie filling pushing it to the edges to seal. Bake until the meringue is browned, 10-12 minutes. Let cool at room temperature for at least 3 hours to set before slicing.