Fry the onions until brown in 2 tablespoons butter. Cook the cubed potatoes in simmering water for 15 minutes. Use 1/2 cup of potato water to rinse out the corn cans. Warm the milk and cream in a large pan and add the potatoes, onions, corn, 1/4 cup butter, herbs and water. Heat mixture to piping hot but don't boil. Then set the kettle aside to cool for a couple of hours. Reheat to piping hot just before serving. Serves 6-8.