In a 2 qt. measuring cup, combine butter and peanut butter. Microwave on full power, 1 1/2-2 1/2 minutes or until melted. Blend well. Mix in crumbs and sugar until very stiff. Add dry milk, too. Press firmly in 9x13 inch pan that has been sprayed with non-stick cooking spray. In small bowl, combine chips and shortening. Microwave on full power, 1-1 1/2 minutes or until chips are soft. Blend well. Pour over bars, spreading carefully. Cool 1/2 hour in refrigerator, then cut into bars. Does not need to be stored in refrigerator.