Preheat oven to 130 degrees C.
Place ham cut side down in a roasting dish. Lightly slice a diamond pattern into the outside of the ham.
Drain pineapple juice from tin into a bowl and stir in the brown sugar. Pour this mixture over the ham. Using the toothpicks, pin the pineapple rings to the ham (eating every third one seems to be the method that works best for me). Press the cloves into the ham. Cover.
Bake in oven for 2- 2 1/2 hours, basting occasionally. Rise temp to 190 degrees, remove lid and cook for an additional 15 minutes.
Last year I used more cloves and used them to pin the pineapple to the ham. This made the pineapple inedible and the ham taste to clovey (It looked beautiful though). So use cloves sparingly. You can pin glace cherries in the centre of the pineapple rings if you are keen on them (as you can see, I am not).