Prepare the garlic butter first, you can do this the day before. To do this, warm the butter in a bowl, add the spices and parsley and stir everything well. Then spread on a piece of baking paper and roll up. Chill the roll in the refrigerator.
Peel the potatoes and cook in lightly salted water for about 15 minutes. Cut the peppers, onions and the boiled potatoes into strips or slices. Wash the meat, pat dry and also cut into strips.
Heat the olive oil in a large, deep pan and sear the steak strips on both sides. Salt and pepper thoroughly and remove from the pan. Fry the vegetables and potatoes in the same oil for about 5 minutes.
Reduce the heat and add the herb butter to the vegetables to taste and toss. Season with salt, pepper and marjoram. Add the meat to the vegetables and let it steep for about 2 minutes.