Remove membrane covering the bony side of the ribs. Place ribs in a covered roasting pan or Dutch oven, meaty side up.
Sprinkle with salt and pepper, dress with lemon slices and sprinkle over the onions.
In a medium bowl whisk the chili sauce, mustard powder, brown sugar, molasses, orange juice and lemon juice.
Pour half of the mixture over the ribs, cover and bake for one hour, basting once with another spoonful of the sauce.
Remove lid and continue to bake for another 45–60 minutes, basting a few times with remaining sauce and pan sauces. Slice into individual ribs and serve.
BARBECUE VERSION To finish these ribs on the barbecue, lift them out of the pot after about 1 ½ hours, shake off excess sauce and grill over medium heat for 3–4 minutes per side, basting with remaining sauce. Cut into individual ribs and serve.