2 packages (.75 to .88 ounces each) mushroom or brown gravy mix
1/3 cup all-purpose flour
1/2 teaspoon salt
1/2 teaspoon black pepper
1 cup beer
Chopped fresh parsley (optional)
Prepare pot roast vegetables: cut potatoes in half (or into quarters if large), onions into 1/2-inch wedges, and carrots and celery into 2-inch pieces; set aside.
Combine gravy mixes, flour, salt and pepper in large bowl. Add vegetables to bowl; toss to coat well. Remove vegetables from flour mixture and place in 5 to 6-quart slow cooker. Add beef roast to bowl, turning to coat evenly with flour mixture. Remove roast and place in slow cooker in center of vegetables.
Whisk beer into remaining flour mixture until smooth; add to slow cooker. Cover and cook on LOW 10 to 11 hours, or on HIGH 6 to 7 hours, or until beef and vegetables are fork-tender. (No stirring is necessary during cooking.)
Remove roast and vegetables. Skim fat from gravy. Carve roast into thin slices. Serve with vegetables and gravy. Sprinkle with parsley, if desired.