Beat the crust butter and cream cheese until smooth. Mix in flour and 1/8 teaspoon salt; divide into 24 balls and refrigerate for 30 minutes, additional to active prep time.
Heat the oven to 350°F. Press each dough ball across the bottom and up the sides of a well in a 24-cup mini muffin pan, keeping the walls even.
Whisk egg, brown sugar, melted filling butter, vanilla and remaining salt. Put a little chopped pecan in each shell, divide the filling among them without filling past three-quarters, then add the remaining pecans.
Bake for 22 to 25 minutes, until the pastry edges are golden and the filling is puffed and set.
Cool in the pan for 15 minutes, loosen the edges with a thin knife and lift onto a rack to cool completely.