Cut the potatoes into large cubes.
Finely chop the onion.
Cut the mushrooms into quarters.
Finely chop the dill.
Pour water into a saucepan, add potatoes and put on the fire. Bring to a boil, reduce heat and leave the potatoes to cook.
Heat a frying pan with a little vegetable oil, add the butter, melt it, then add the onion. Fry, stirring occasionally, over medium heat for 3 minutes.
Add the sliced mushrooms to the onion, stir and continue frying for about 7-10 minutes until the mushrooms are cooked.
Add fried onions and mushrooms to the potatoes, pour in the cream and stir.
Add dill to the soup, salt and pepper to taste. Cook for another 5-7 minutes until the potatoes are soft. Remove from heat and serve.