Melt 3 tablespoons of the butter in a pan add the onion and cook over low heat, stirring occasionally for 10 minutes until lightly browned

Meanwhile, bring the milk to just below simmering point in another pan, then remove from the heat

Stir the polenta flour into the onion and cook, stirring constantly, for 2-3 minutes

Gradually stir in the warm milk and 2 1/2 cups warm water

Season with salt and pepper to taste and cook for 1 hour

Stir in the cream, the reamaining butter and the parmesan and serve