1. Slice the fish into thin strips, about 1cm wide. Season with salt and pepper.
2. Whisk the eggs and milk together. Dust the fish in the flour and shake the excess off. Dip in the egg and milk, then roll in the breadcrumbs. Dip back into the egg and again through the breadcrumbs. Place in the fridge to firm up.
3. To make the tartare sauce, stir all the chopped ingredients into the mayonnaise. Season to taste. It should be coarse, thick and pungent.
4. Heat a fat-fryer to 170°C (or warm the vegetable oil in a pan using a probe to gauge the temperature accurately) and cook the fish fingers for 5 minutes, until brown and crispy. The fish will cook quite quickly, and it's better to be just done than dry and mushy. Remove and season.
5. Spread the bread liberally with tartare sauce. Add a layer of fish fingers and a few leaves of baby gem. Give the whole thing a quick squash and eat whilst looking at a rainy window and thinking the world isn't so bad when you've got a fish finger sarnie.
Recipe courtesy of Waitrose