First make the sauce: Peel and chop the onion. Halve the grapes.
Pour the wine into a small saucepan and put over a low heat. Add the other ingredients, stir and gently bring to a simmer. Cook uncovered for about 35 minutes, stirring every few minutes, until it reduces by about ⅔ rds.
Season the venison steaks on both sides with salt and pepper then rub in a little sunflower or rapeseed oil.
Put the griddle pan over a high heat quickly to seal both sides of each steak then turn down and cook for about 3 (rare) or 4 (medium) minutes on each side.
Pour over the sauce, mix with the meat juices. Serve with the vegetables of your choice and a mash - mashed potato & fennel goes very nicely with it.