Tangy Spare Ribs

• 1 onion
• 1/8 peper
• 1,300 gr pork spare ribs
• 240 ml ketchup
• 240 ml water
• 60 ml lemon juice
• 50 gr celery (finely chopped)
• 30 ml vinegar
• 28 gr butter
• 28 gr brown sugar