For the venison, tie the venison up with kitchen string - this will help it to retain its shape. Rub with olive oil and season with salt and freshly ground black pepper.
Heat a frying pan and sear the venison until browned on all sides. Add a knob of the butter, reserving the rest for the crust, and brush the meat with the melted butter. Turn down the heat and add the garlic and half of the thyme. Fry gently for about ten minutes. Remove from the pan and leave to rest for five minutes, then remove the string and slice thinly.
For the garlic potato wedges, place the chopped potato into an ovenproof frying pan with the vegetable oil and garlic and fry for five minutes, turning frequently, until lightly golden-brown on all sides. Place into the oven and roast, shaking the pan from time to time, for 15 minutes, or until golden-brown on all sides. Remove from the pan and drain on kitchen paper.
For the sauce, place the pan used to cook the venison back onto the heat, add the onion and cook gently until softened. Add the wine and bring to a simmer, scraping up the bits from the bottom of the pan with a wooden spoon. Add a splash of boiling water and simmer for 3-4 minutes, or until reduced slightly. Add the cream, season with salt and freshly ground black pepper and stir.
To serve, place the wedges onto a serving plate, top with the sliced venison and pour over the sauce. Garnish with fresh parsley leaves and serve.