Cut ribs to smaller pieces (with about three to four ribs per piece)
Rub ribs all over with the mustard mix. Allow to marinate for 30 minutes at least.
In a large pan, heat a little oil over a high heat.
Sear ribs in batches until browned.
Put browned ribs on an oven tray. Cover with baking paper, then aluminium foil.
Bake in the centre of oven for about 2 hours.
In the ribs pan, add a splash more oil and fry the onion and garlic.
Add the butter and fry in, then add remaining ingredients and stir well.
Allow to cook over a medium heat for about five minutes, then strain carefully through sieve.
Return to the pan and reduce for a further five minutes until thick and syrupy.
Turn oven up to 220°c
After initial cooking time, carefully uncover to avoid steam, and transfer to a chopping board. (allow to cool for a few minutes so you can handle them) Cut the ribs into single ribs, return to oven tray and coat with the sauce, cook for 10 more minutes or so in the hot oven.