Best Ever Slow Cooker Italian Beef Roast

INGREDIENTS

• 1 (3 pound) beef chuck roast
• 1 onion, quartered
• 1 (10.5 ounce) can beef broth
• 1 (1 ounce) packet dry au jus mix
• 1 (.7 ounce) package dry Italian salad dressing mix (such as Good Seasons®)
• 1/2 teaspoon salt
• 1/2 teaspoon ground black pepper