Crack the egg into a bowl, and whisk well as you add the oils, Parmesan and lemon juice. If you're not going to add an anchovy or two, whisk in the salt.
Break the crisp lettuce into bite-sized pieces and put into a salad bowl. Drop in the shredded cold chicken, mix to combine and season with pepper, to taste.
Toast the tortilla chips for a couple of minutes in an oil-less pan over a medium heat.
Give the dressing another whisk, pour it over the salad and toss to mix. Add the tortilla chips (and some anchovies, if you like) and toss again before wolfing down.
Recipe from Nigella: Kitchen by Nigella Lawson (published by Chatto & Windus).