Add 100g of butter and the truffle oil. Mix well and cover with foil or a lid and set aside. Take the venison fillet out of the cling film over a plate, squeezing out all the excess marinade from the cling film. In a hot, lightly oiled frying pan, sear the venison on each side for 30 seconds. When done, deglaze the pan with Maille Sauternes white wine vinegar and maple syrup, add the extra marinade, lower heat and cover with a lid. Simmer for 2 mins, take the fillet out, wrap in foil and keep warm.