In a medium bowl, cream together butter and cream cheese until smooth. Stir in flour until well blended. Roll dough into 1 inch balls and press into mini muffin cups to form little crusts.
In another bowl, mix together brown sugar, pecans, melted butter, eggs, and vanilla. Spoon filling into each crust, filling almost to the top.
Bake for 20-25 minutes, or until the filling is set and the crust is lightly browned. Cool in pans on wire racks.