Mix mayonnaise and double cream together and add walnut oil and seasoning to taste. (If dressing becomes too thick add a little water). Put to one side for later.
Roughly chop chervil - you will use this for garnish later.
Trim and wash the leeks, keep them whole.
Bring a large pan of salted water to the boil, then add the leeks. Cook for 2 to 3 minutes then remove and put in a bowl of iced water to refresh.
Remove from water once refreshed and cut into 5cm sticks.
Melt a knob of butter in a pan and then add the leeks, cook gently for 2 to 3 minutes then remove and allow to sit.
Bring a small pan of water with a dash of vinegar to the boil and create a water whirlpool using a wooden spoon. Break your eggs and slowly add to the centre of the whirlpool. Leave for 3 to 4 minutes depending on how soft or hard you prefer your yolk, then remove and dry with a paper towel.