Barbecue Beef Sandwiches

• 1 garlic clove
• 1 hamburger buns
• 1,400 gr beef rump roast
• 425 ml tomato sauce
• 75 gr brown sugar
• 60 gr onions
• 30 ml lemon juice
• 24 gr flour
• 16 ml beef instant bouillon
• 6 gr chili powder