Heat oven to 350°F. Grease 13x9-inch pan. In large bowl, combine cake mix, margarine and 1 egg; mix well with pastry blender or fork. Press mixture in bottom of greased pan. Bake at 350°F. for 7 minutes.
Meanwhile, in medium bowl, combine condensed milk, vanilla and 1 egg; mix well. Stir in toffee bits and pecans.
Remove pan from oven. Pour filling evenly over warm base. Return to oven; bake an additional 22 to 30 minutes or until filling is set. Cool 1 hour or until completely cooled. Cut into bars. Store in refrigerator.