Step 1

Begin by making the sriracha, as it takes 4–6 weeks to ferment. Remove the green stalk from the chillies, cut into small pieces and place into an air tight container with the garlic. Create a 2% brine by weighing how much water you need to cover the chillies, then calculating 2% of that weight and adding that amount of salt. Cover the chillies with the brine, then lay a sheet of parchment over the top and put a small plate on the top to keep it all submerged. Label the container with the date and leave to ferment for 4–6 weeks

Step 2

Once fermented, transfer to a blender with the stage 2 ingredients and blend until very smooth. Pass the sauce through a fine sieve into a large pan and bring to the boil– this will stop the fermentation. Chill down the sauce overnight, then taste and adjust seasoning. Store in the fridge

Step 3

To make the green oil, blanch the greens separately until tender. It is important to take the time to blanch them separately as they have different cooking times, e.g parsley takes 5 seconds, whereas fibrous leek tops would take up to 2 minutes. Submerge in iced water to preserve colour, then squeeze out as much water as possible

Step 4

Weigh the blanched greens, then place into a blender with double the weight in rapeseed oil. If using a thermomix, blend on speed 8 at 70ºC for 7 minutes. If using a regular blender, blitz at the highest speed for about 10 minutes. Pass through a sieve lined with a muslin cloth set over a bowl and leave to drip overnight, then transfer to a squeezy bottle

Step 5

Preheat the oven to 180ºC/gas mark 4

Step 6

For the butter emulsion, place the water into a small pan and gently heat. Gradually add the chilled, cubed butter, bit by bit, whisking to emulsify. Once all of the butter is fully melted and emulsified, blitz with a hand blender to fully incorporate

Step 7

Whisk through the sriracha one spoonful at a time, until it is a light orange colour (you can adjust the heat to your preference). Keep warm and set aside

Step 8

In a large pan, heat rapeseed oil until nearly smoking hot, then sear the cod’s head flesh side down. Leave to sear, pressing down on the head to achieve even colouring. Once seared, place in the oven for 5–10 minutes. Leave to rest for 5 minutes

Step 9

Dress the fish with salt, pepper and lemon juice before placing the cod’s head on a large plate and generously pour over sriracha butter sauce. Finish by splitting the sauce with a drizzle of bright green oil