Omit boiling the ham altogether if using a pre-cooked ham. Wash ham and cover with boiling water and let cook on top of stove for 4 hours. Let ham stand in liquid over night.
Next day remove the fatty rind, make gashes across the surface of ham and stick in whole cloves.
Make a paste of the sugar, flour and mustard by adding the syrup and water. Use water in which ham was cooked if available. Spread over ham and place in roasting pan. Bake uncovered at 400-F for 45 minutes.