Melt 5 tablespoons butter in a heavy saucepan.
Over medium heat, stir in flour, forming a smooth paste.
Stir in sugars.
Heat, stirring constantly, until sugars are melted and mixture is smooth.
Stirring constantly, gradually add 1/2 cup of the hot milk; continue stirring until mixture boils.
Add the remaining milk, 1/2 cup at a time, stirring constantly; bring to boiling after each addition.
Vigorously stir about 3 tablespoons of the hot mixture into the egg yolks.
Immediately return to mixture in saucepan.
Cook about 3 minutes, stirring constantly.
Remove from heat and stir in the salt, extract, and remaining butter.
Set aside to cool.
Turn filling into the pastry shell.
Top with meringue and bake as directed in meringue recipe.
Cool completely before serving