Dab steaks dry, season with salt. Wash the rosemary, shake dry and chop coarsely. Heat 1 tablespoon of oil in a frying pan. Briefly sear the steaks on both sides, sprinkle with rosemary.
Remove and place in an ovenproof dish. Cook in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 5-8 minutes.
Clean and wash the chard and cut it into leaves. Cut the stalks off the leaves and cut into fine strips. Peel and finely chop the onion. Wash, halve and seed the grapes. Heat 2 tablespoons of oil in a large frying pan, fry the chard and onion for 2-3 minutes, turning them over.
Add chard leaves and stock and simmer gently for 4-5 minutes. Remove meat from the oven and keep warm. Add grapes to the chard and fry for another 2-3 minutes, season with salt and pepper.
Sprinkle meat with sea salt and coarse pepper and arrange on plates with the chard and grape vegetables.