Sauté the leek in oil, butter and chili. Add the bay leaf spice, rosemary and the finely sliced carrot, then the chopped garlic. Stir everything well, deglaze with water and add the peeled, diced tomatoes. Cover and cook for about ten minutes. Next, add the white wine, the stock, the chervil and the finely chopped fennel bulb.
Simmer gently for another ten minutes with the lid open at a low temperature. Meanwhile, rinse and dry the fillet and cut into bite-sized morsels. Roll in salt and pepper, then in cornstarch (maize starch). Place the pieces on top of the sauce and steam covered for about ten minutes at low temperature. Finally, add the cream and grate in half the tonka bean. Cover and simmer for about half an hour. Season with pepper and a little salt.
Serve with basmati rice and a full-bodied, but dry white wine.