Beat crust butter and cream cheese smooth. Mix flour and 1/8 teaspoon salt; form 24 balls. Refrigerate 30 minutes, additional to active prep time.
Heat oven to 350°F. Press balls evenly across bottoms and up sides of 24-cup mini muffin pan.
Whisk egg, sugar, filling butter, vanilla, and remaining salt. Add some pecans per shell; divide filling without exceeding three-quarters full. Add remaining pecans.
Bake 22 to 25 minutes until pastry edges golden and filling puffed and set.
Cool in pan 15 minutes; thin-knife loosen edges. Rack-cool completely.