Peel the potatoes and boil them in salted water for about 15 minutes. Cook peas in boiling salted water for about 6 minutes. Drain. Clean, wash and slice the tomatoes.
Season vinegar with salt and pepper and add 1 tablespoon of oil. Mix tomatoes and salad dressing and sprinkle with chives. Heat the remaining oil in a small pan and fry the sausage snail in it until golden brown on both sides.
Drain the potatoes and mash them with a potato masher. Add milk and mix. Season to taste with salt and pepper. Add peas and fold in. Arrange pea puree and sausage snail on a plate and serve garnished with parsley as desired.
Serve with tomato salad and mustard.