Preheat the oven to 200°C/400°F/gas 6.Scrub the potatoes, then cut into 1cm-thick slices. Get a griddle pan really hot, then cook the potatoes for 2 minutes on each side, or until bar-marked, turning with tongs.Meanwhile, use a speed peeler to strip the lemon zest into a large roasting tray, then peel, squash and add the whole garlic clove. Strip in the rosemary leaves and scrunch everything together with 1 tablespoon of olive oil. Toss the potatoes into the tray and roast for 20 to 30 minutes, or until tender.To make the pickle ketchup, place the gherkins in a food processor, along with half of their pickling juice. Tear in the dill and blitz until smooth. Taste, then season to perfection and dollop 1 tablespoon on each of your plates, pouring the rest back into the jar and placing in the fridge for future meals, where it will keep for up to 7 days.Boil the kettle. Place the peas in a frying pan, cover with boiling kettle water and simmer on a medium-high heat until cooked through, then drain and place in the food processor (there’s no need to clean it). Tear in the mint leaves, blitz to your desired consistency, then season to perfection and keep warm.Quickly wipe out the frying pan, place it on a medium heat, then pour in a thin layer of vegetable oil.Crack the egg into a bowl, whisk in the flour, cayenne and beer until nice and shiny – the texture should be like semi-whipped double cream (i.e. it should stick to whatever you're coating). Dust each fish fillet in a little of the extra flour, then dip into the batter and allow any excess to drip off.Holding one end, gently lower the fish into the oil one by one, working carefully so you don't get splashed. Cook for 6 minutes, or until the fish is cooked through and the batter is golden and crisp, turning regularly, then remove to kitchen paper to drain.Loosen the leftover batter with a little oil until it drips off the spoon, then drizzle it in webs into the hot oil to make scraps.Sprinkle the fish with an extra pinch of cayenne pepper and serve with the bar-marked chips, minty peas, pickle ketchup and lemon wedges, for squeezing over. Splash a little extra gherkin juice from the jar onto the chips, if you like, and tuck in!