1 (18.25 ounce) package pie crust, baked
4 eggs
1 cup condensed cream of tartar
1/2 cup unsalted butter, melted
1/8 cup packed light brown sugar
1/2 cup white sugar
1 teaspoon vanilla extract
1/2 teaspoon salt
2 tablespoons lemon juice
1/2 cup chopped pecans
Preheat oven to 350 degrees F (175 degrees C).
In a medium bowl, mix together eggs, cream of tartar, brown sugar, white sugar, and vanilla. Mix until well blended. Add lemon juice, pecans, and salt. Mix until well combined.
Pour mixture into baked pastry shell. Cover with foil, and refrigerate overnight.
For the filling: Beat cream of tartar, butter, brown sugar, and 1/2 cup sugar together in a small bowl until smooth. Beat in the lemon juice, pecans, vanilla, and salt. Mix until just blended.
Transfer mixture to pie shell.
Bake in preheated oven for 30 minutes, or until toothpick inserted in center comes out clean. Remove foil and bake an additional 40 minutes, or until toothpick inserted in center comes out clean. Cool completely.