For the venison cutlets, season the cutlets with salt and freshly ground black pepper.
Place the polenta and rosemary into a bowl and mix well.
Rub half the olive oil into the venison cutlets, then dip the cutlets into the polenta and rosemary mixture to coat each side.
Heat a frying pan until hot, then add the remaining olive oil and the polenta-encrusted venison. Cook for 2-3 minutes on each side, or until golden-brown and cooked to your liking. Remove from the pan and leave to rest in a warm place.
For the polenta, place the water, milk, salt, black pepper and garlic into a heavy-based pan. Place the pan over the heat and bring to the boil.
Add the polenta and begin to stir. Cook for 1-2 minutes, stirring constantly so it doesn't stick to the pan or become lumpy.
Add the double cream and cook for one minute.
Add the mascarpone, parmesan, flatleaf parsley and truffle oil and stir well. Cook for one minute then remove from the heat.
Heat a frying pan until hot. Add the olive oil and mushrooms and fry for 3-4 minutes, or until golden-brown.
For the pesto, place all of the pesto ingredients into a pestle and mortar and pound to a paste. (You may place into a food processor and blend if preferred.)
To serve, spoon the polenta into the centre of each plate and top with equal amounts of mushrooms. Place three cutlets to the side of each pile of polenta and finish with a spoonful of pesto drizzled around.