We had spare ribs on Saturday. A 750g rack provided enough for three people.
There are marinade recipes here and here. This time, I used about 3tbsps of tomato ketchup, a dstsp of soy sauce, a tbsp of sunflower oil, two cloves of garlic crushed with salt, and the juice of half a lemon. I spooned the marinade over the meat, which I left out in a roasting tin covered with foil for a couple of hours.
As I have written before, this cut of pork benefits from slow cooking. It remains juicy; and there is the additional benefit that the marinade does not burn.
I put the roasting tin -- foil removed -- on the lowest shelf of the oven, set at gas mark S/130C, and left it for three and a half hours, turning the meat a few times. I let the meat rest out of the oven for 10 minutes before carving it into separate ribs.