Wash the potatoes and cook in plenty of boiling water for about 20 minutes. Drain, rinse, drain and remove the skin. Meanwhile, wash the thyme, shake dry and, except for something to garnish, pluck leaves from the stems.
Clean and wash the onions and cut approx. 1/3 of the green into rings. Wash, clean and halve the tomatoes. Press potatoes through a potato ricer. Mix eggs and flour into the potatoes. Season with salt, pepper and thyme.
Crumble the cheese and carefully fold into the dough. Form 8 meatballs from the mixture. Heat 2 tablespoons of oil in 2 pans. Fry the meatballs and tomatoes over medium heat for about 5 minutes on each side.
Keep finished meatballs warm in a pan. Fry the onions and thyme stems in the cooking fat in the freed pan for approx. 3 minutes, turning them over. Season with salt and pepper. Arrange meatballs, onions and tomatoes on plates.
Garnish with thyme.