Empty cookie mix into a large mixing bowl; stir to combine. Add 1/2 cup softened butter, 1 slightly beaten egg and 1 teaspoon vanilla extract; mix until completely blended.
Roll dough into walnut-size balls. Place 2 inches apart on a lightly greased cookie sheet. Press cookie down slightly with the heel of your hand. Bake at 350 degrees F for 11 to 13 minutes or until edges are lightly browned.
Cool for 5 minutes on baking sheet. Remove to wire racks to cool completely.
Yields 2 1/2 dozen.