Trim off any visible exterior fat from the meat and place it into a 5-6 quart slow cooker. Peel and slice the onion as thin as possible and put it on top of the meat. Mix the dry dressing mix with the hot water until completely dissolved; pour over the meat and onions.
Put cooker on LOW, cover and cook for about 8 hours or until the meat easily shreds with a fork. There will be lots of good juice in the cooker. Take meat out and shred. Serve as a sandwich on hard crusty rolls (think Breadsmith here) with some of the onions on top and the au jus to dip into. SPICY VARIATION: Instead of the Hidden Valley dressing and water, use an entire bottle of peperoncini (spicy Greek or Italian pickled peppers). Pour them into the cooker along with their juice, on top of the meat and onion, and cook as above. Serve with some of the onions and peppers on each sandwich.
Submitted by: Sandy Olson, Palm Shadows