Wash the fillet, dab dry, cut a deep pocket into it. Clean and wash the tomato, cut off 2 slices. Remove seeds from remaining tomato, dice flesh. Cut cheese into small pieces. Fill fillet with cheese, tomato slices and sage.
Pin up if necessary. Clean, wash and halve the mushrooms. Pluck thyme leaves. Peel and finely dice the shallot. Heat the oil. Fry the fillet in the oil until golden brown all around. Season with salt and pepper. Add shallot and mushrooms, fry for another 5 minutes and season. Deglaze with stock, add cream, peas, thyme and diced tomatoes. Bring to the boil briefly and thicken with sauce thickener to taste.
Fry the fillet in the oil until golden brown all around. Season with salt and pepper. Add shallot and mushrooms, fry for another 5 minutes and season. Deglaze with stock, add cream, peas, thyme and diced tomatoes. Bring to the boil briefly and thicken with sauce thickener to taste. Season to taste with salt and pepper and serve. Tastes good with mashed potatoes