Cook for a couple of minutes then add the tomato puree. Season with salt and pepper and cook until all the liquid is absorbed. Remove from the heat and add all the chopped herbs, adjust seasoning, if necessary Grease a baking tray with melted butter and cut the polenta sheet so it fits neatly into the greased tray Top the first sheet of polenta with a spoonful of the vegetable ragout and a generous sprinkle of grated Grana Padano Riserva. Alternate the polenta, vegetable ragout until the tray is filled to the top Add the grated Grana Padano Riserva and drizzles of melted butter to the top layer. Bake for about 20 minutes and serve with fresh lettuce.