To make the Tartare Sauce, whisk the egg yolks, mustard and vinegar in a bowl. Slowly add the oil, drop by drop at first, then, when it begins to thicken, in a slow, steady stream, whisking all the time until it begins to thicken like mayonnaise. Stir in the anchovy essence, chopped gherkin, capers and parsley into the sauce and season to taste with salt and pepper. Stor