Just in from the man himself :-)

The tartare sauce is so quick and simple. The quantities are not set in stone but here's what I do:
You need a handful of little cornichons, maybe six or seven, a tablespoon and a half of nonpareil capers (the little ones), rinsed, a tablespoon or more of finely chopped fresh parsley, a tiny squeeze of lemon (needed but don't overdo it), five tablespoons of mayo (full-fat Hellmans for me!) and seasoning to taste.

Chop the cornichons and capers very finely on a board then just mix everything together in a bowl. Chill, then voila! Too thick? Add more mayo.

Enjoy :-)