First make the mayonnaise by blending together the eggs, mustard and salt in a liquidiser. Trickle in half the oil very slowly until you have a thick emulsion, then add the lemon juice and slowly add the remaining oil. Stir in the tarragon.
Brush the venison fillets with the oil and season. Chargrill or fry in a hot pan for 3 minutes each side for rare steaks or until cooked to your liking. Serve with the hot chips and mayonnaise.