Spare ribs can be tough if not cooked properly. Slow cooking spare ribs will get you a rib as tender as baby back ribs every time. If you want to put these on the grill, start them out in the oven first, then put them on the grill for the last hour.
Line two medium or one large baking tray with foil. If you have a large baking tray, you will be able to fit the slab of ribs on one baking tray. If you have the regular sized baking trays, you will need two. If you are using the smaller baking trays, cut the ribs in half, and place one half on each baking tray.
Preheat oven to 121 degrees C.
Pour the barbecue sauce into a large bowl. Fill each bottle 1/8 full with water. Shake vigorously. Pour this into the bowl with the barbecue sauce. This helps get the rest of the barbecue sauce out of the bottle. It will not significantly thin the sauce.
Add the garlic powder, onion powder, salt, pepper, Cajun seasoning, hot sauce, ketchup, mustard and brown sugar. Mix thoroughly.
Coat the ribs. Using a spoon or a basting brush, coat the undersides of the ribs. Flip them over and coat the top of the ribs.
Put the ribs in the oven. If you are using the medium sized baking trays, put them in lengthwise in the oven. They will just fit. Make sure they are as far back as they can go into the oven, or else the oven door will not shut.
Bake for 2 hours at 121 degrees C. Baste the top of the ribs after 2 hours.
Turn the temperature down to 93.3 degrees C. Baste the ribs every hour and cook for 3 hours.
Turn the heat up to 121 degrees Cor the last hour. Baste.
Remove ribs from oven or grill and let set for 10 minutes. Cut ribs individually or into serving sizes of three to four ribs per serving.
Change they type of barbecue sauce to fit your taste.
Always wash hands after touching raw meat.