1. Rinse beef stew meat, and pat dry. Sprinkle with salt and pepper; toss in flour, shaking off excess.
2. Cook half of beef in 2 Tbsp. hot oil in a Dutch oven over medium-high heat, stirring occasionally, 10 minutes or until browned. Repeat procedure with remaining beef and oil. Stir in tomato paste; cook 1 minute. Add broth, and stir to loosen particles from bottom of Dutch oven. Transfer mixture to a 6-qt. slow cooker.
3. Stir in celery, onion, and garlic. Top with butternut squash. (Do not stir to incorporate.) Cover and cook on LOW 4 1/2 hours or until meat is tender. Serve over hot cooked mashed potatoes, if desired. Garnish, if desired.