In a large bowl, cream together the butter and 0.5 cup powdered sugar until light and fluffy. Beat in vanilla.
Gradually add the flour and pecans, mixing until just combined. Do not overmix.
Roll dough into 1-inch balls and place on ungreased baking sheets.
Bake for 10-12 minutes, or until lightly golden.
Let cool slightly, then roll in remaining powdered sugar while still warm. Cool completely on wire racks. Dust with more powdered sugar before serving.
Notes
These cookies are best stored in an airtight container at room temperature.