• Heat 20 g of butter and 2 table spoons of olive oil in a large pan and fry the onions on a medium heat until golden brown. Add the thyme leaves and cook for a couple of minutes.
• Remove the onions and set aside in a bowl to cool. Add the remaining butter, breadcrumbs, hazelnuts and parsley and mix well. Season with salt and pepper.
• Season the lamb filets with salt and pepper. Heat the remaining olive oil in a pan and fry the meat on a high heat from all sides to seal it. Place the meat in a flat oven proof dish. Spread the hazelnut mixture on top.
• Place the lamb in a preheated oven for about 210 degrees Celsius. Bake for about 20 minutes until golden brown.

For the Sauce

• While the lamb is in the oven add the Balsamico and Sherry into a saucepan and bring to boil. Add the chickenstock and boil for 2 minutes. Now mix in the 2 table spoons of corn flour with a whisk. You can add more corn flour if you prefer a thicker consistency. Season with salt and pepper.
• Before serving drizzle the sauce over the lamb. Serve with potatoes and green vegetables.