Combine cream cheese and margarine, mixing well until blended. Add flour. Mix well. Chill. Divide dough into quarters. Divide each quarter into 12 balls. Press each ball onto bottom and sides of miniature muffin pans.
Combine eggs, brown sugar and vanilla. Stir in pecans. Spoon into pastry shells, filling each cup. Bake at 325 F for 30 minutes or until golden brown. Cool 5 minutes. Remove from pans. Sprinkle with powdered sugar, if desired.