Season the venison with the black pepper, then rub with olive oil.
Place in the frying pan and cook for 4-5 minutes on each side until golden brown and medium rare in the middle.
At the last minute, add the butter to the pan and baste the meat. Remove from the pan and leave to rest in a warm place.
Whilst the meat is resting, pour off any excess fat in the pan, just leaving around 1 tbsp. Cook the shallot in the left over fat.
Roughly chop the rehydrated porcini mushrooms, reserving the water that they have soaked in. Add the brandy to the pan to deglaze it. Cook for 1 minute, then add the chopped mushrooms and around 4 tbsp of the water the mushrooms soaked in. Simmer until reduced by half, then add the double cream. Simmer for 2 minutes and season with salt and pepper.
Heat another frying pan on a high heat and add 25g of butter and the sliced mushrooms. Cook until coloured, then add in the rosemary. Fry for a further minute then remove from heat.
Take the rested venison and cut into 2cm slices and serve with the brandy and porcini sauce and sauté mushrooms