Peel, wash and slice the potatoes. Heat 2 tablespoons of oil in a large pan. Fry the potatoes for about 20 minutes while turning. Season with salt and pepper. Peel onion and garlic and chop finely.
Heat 1 teaspoon of oil. Fry the onion and garlic in it. Add the spinach and 100 ml of water and cook covered for about 16 minutes. Season to taste with salt, pepper and nutmeg. Cut herb butter into 5 slices.
Wash the meat and dab dry. Heat 1 tablespoon of oil. Fry the meat for 2-3 minutes on each side. Season with salt and pepper. Add 1 slice of herb butter and melt. Turn the meat in it.
Add rosemary to the potatoes 5 minutes before the end of the frying time. Arrange everything. Spread the remaining herb butter on the lamb. Garnish with lemon slices and rosemary.