Combine all the gremolata ingredients in a small bowl and set aside.
Pour the stock and milk into a large pan and bring to a simmer. Gradually whisk in the polenta, stirring continuously to avoid lumps. Cook for around 5 minutes or until smooth and creamy, then stir in the cheeses until melted. Add the butter and herbs and season with salt and pepper.
In a frying pan, heat the olive oil over a medium setting. Add the mushrooms and garlic and fry for a few minutes until the mushrooms are tender. Season with salt and pepper.
To serve, spoon the polenta on to warm plates, top with the sautéed mushrooms and drizzle the gremolata over.
Recipes and photographs taken from Life's too Short to Stuff a Mushroom by Prue Leith, photography by Ant Duncan, (Carnival, £25)
