For mushrooms sauce:
1 onion, diced
250 gr chestnut mushrooms, sliced
125 ml vegetable stock
125 ml cream
1 table spoon of sour cream
1. drain the liquid out of the grated potatoes and onion, add to a bowl with the egg, flour, and season with salt and pepper.
2. Heat the oil in a frying pan and bake about 3 small pancakes on each side for 2 to 3 minutes. Drain on kitchen paper. Serve or store in tinfoil in a low heated oven till ready to serve.
3. in a frying pan add oil and sweat the onion till soft, add the mushrooms, cook them for 5 minutes and add the stock, let simmer. Add the cream with the sour cream and serve warm.