Peel, wash and quarter the potatoes. Cook in boiling salted water for about 20 minutes. Add peas 5 minutes before the end of cooking time. Wash and finely chop lemon balm.
Heat milk and melt butter in it.
Drain the potatoes and peas, remove some of the peas and put the rest with the potatoes through the press. Stir in milk, lemon balm and whole peas, season with salt and pepper.