Defrost the soybeans. Whisk the butter until whitish-creamy with the whisk of the hand mixer. Wash the thyme, set aside 4 stems. Remove the coarse stems from 6 stems. Chop the rest finely.
Coarsely chop about 3 tablespoons of soybeans. Stir the egg yolks, breadcrumbs, chopped soybeans and thyme into the butter. Season to taste with salt and pepper. Form a roll (approx. 4 cm Ø) from the mixture using cling film.
Allow the roll to set in the freezer for approx. 20 minutes. Wash the meat and dab dry. Season with salt and pepper. Heat oil in a coated pan. Fry the meat in the pan for about 4 minutes until golden brown.
Remove meat from the pan. Remove the foil from the roll. Cut thin slices (approx. 0.5 cm) from the roll and cover the meat with them. Press the crust lightly. Cook the meat in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 12 minutes.
Prepare mashed potatoes according to the instructions on the packet. Fold the remaining soybeans into the mashed potatoes. Wash the tomatoes and dab dry. Heat the roasting pan again and sauté the tomatoes and thyme stalks for about 2 minutes.
Take the meat out and cut into slices. Arrange meat and puree on preheated plates, garnish with thyme and 1 tomato each.