Clean and chop the onion and garlic. Put the olive oil and butter in a pan, sauté the onion, garlic, rosemary and thyme briefly. Add the fillets and sear for 1 minute on each side, season with salt, pepper and remove.
Deglaze with balsamic vinegar, bring to the boil, put the fillets in the pan, turn them briefly, pour the stock over them and place in the oven for 10 minutes at 120 ° C. Arrange the fillets on a large plate with a little stock and drape with fresh herbs.
Tip: Serve with a baguette or lightly salted flatbread.