Fish and chip tortilla

Preheat the oven to 200°C. Spread out the chips in a single layer on a large baking tray. Cook according to the packet instructions, leaving them in for an extra couple of minutes to make sure they are deep golden and crisp, turning halfway – cooking them for longer than normal ensures they hold their structure once folded into the egg mixture. Remove and allow to cool for 5 minutes

Meanwhile, heat the olive oil in a 24cm non-stick frying pan over low heat. Add the onions and a small pinch of salt. Cook gently for 20-25 minutes, stirring occasionally, until completely soft and translucent with no colour – a tortilla should taste sweet and mellow so don’t caramelise the onions as they will dominate and darken the final colour

Add the sherry vinegar and cook for 30 seconds. Remove from the heat and allow to cool slightly

Season the cod with the fine sea salt. Steam gently for 4-5 minutes until just opaque and beginning to flake – it should feel softly resistant when pressed in the centre. Allow to cool slightly, then flake into large, delicate pieces. Alternatively, you can gently poach the cod in lightly salted water at 80-85°C

In a large bowl, whisk the eggs with the double cream, flaky sea salt and white pepper, to taste, until just combined – avoid overwhisking as incorporating too much air will cause a soufflé-like texture rather than a custard-like texture

Fold through the softened onions, warm chips and flaked cod, then allow the mixture to sit for 5 minutes – this resting period allows the chips to absorb some of the egg, creating the iconic soft interior

Wipe out the frying pan and return to a medium-low heat. Add the butter and allow to foam gently

Pour in the egg mixture, spreading it out evenly, and cook it undisturbed for 5-6 minutes. As the edges set, gently push them inwards with a spatula and tilt the pan to allow uncooked egg to flow underneath

When the base is golden and the sides are set but the centre remains slightly loose, place a large flat plate over the pan. Confidently invert the tortilla onto the plate then slide it back into the pan, upside down. Cook for a further 3-4 minutes for a just-set centre

Transfer the tortilla to a board and allow it to rest for at least 10 minutes before slicing

Mix together the parsley, chives and capers and half of the lemon zest with enough olive oil to create a spoonable gremolata, then drizzle some over the tortilla

Mix a little of the lemon juice and zest into the mayonnaise

Sprinkle the remaining zest over the tortilla, slice it up and serve with the lemon mayonnaise, remaining gremolata and lemon wedges