Combine 5 cups water, peas, cloves and cinnamon stick in slow cooker. Cover and cook on HIGH for 3 hours or LOW for 4 hours.
Remove the cloves and cinnamon stick. In a medium-size nonstick skillet, melt the butter over medium heat. Add cumin, 1/2 teaspoon ginger, turmeric, mustard seeds, coriander and cayenne to skillet and cook 1 to 2 minutes, stirring constantly. Stir the spice mixture into slow cooker and continue to cook another 2-1/2 hours on HIGH or 3 hours on LOW.
Carefully puree soup in batches. Just before serving, stir in remaining 1/2 teaspoon ginger, the cream, salt and pepper and serve over rice, if desired.