Rub the mushrooms with kitchen paper or clean them with a brush. Halve the mushrooms. Clean the peppers, cut them in half lengthwise, remove the seeds and wash them. Cut into thin strips. Peel onion and garlic, chop both.
Wash the spinach and spin dry.
Bring milk and 1⁄2 l water to the boil. Stir in stock. Stir in polenta and allow to trickle in. Cook for about 10 minutes at low heat, stirring frequently. Stir in cheese and 40 g butter in pieces, salt if necessary.
Roughly chop the nuts. Roast briefly in a pan without fat, remove. Heat the rest of the butter in the pan. Stir-fry the mushrooms, onion, garlic and pepperoni. Deglaze with vinegar. Season with salt and pepper.
Add the spinach, let it collapse for a moment. Mix in the nuts. Serve with polenta.