Peel onion and garlic. Chop the onion finely, press the garlic through a garlic press. Heat the fat in a pot and fry the onion and garlic until transparent. Add rice, sauté briefly and deglaze with 400 ml broth and wine.
Add a little salt, bring to the boil, cover and allow to swell over a low heat for 20 minutes. Clean, wash, pat dry and quarter the tomatoes. Wash thyme, dab dry and chop. Add the tomatoes and thyme, except for a little bit for sprinkling, to the rice 5 minutes before the end of the cooking time and cook with it.
In the meantime cut the pork fillets into 8 medallions. Heat the oil in a pan and fry the medallions well. Season with salt and pepper and deglaze with remaining stock. Add peppercorns, bring to the boil and simmer covered for 3-4 minutes.
Remove medallions from the pan and keep warm. Stir the sauce thickener and sour cream into the stock, bring to the boil again briefly and season to taste with salt and pepper. Fold the parmesan into the hot risotto, spread on plates and arrange the medallions on top.
Spread sauce over it, sprinkle with remaining thyme and serve garnished with parsley.