Preheat the oven to 190C with the fan on full.
Season the cod with a touch of salt.
Cut the spring onion finely and rinse in cold water. Set aside and allow excess water to drip dry.
Cut the bottom off the spring green and separate the leaves. Wash in cold water.
Bring a large pot of salted water to a boil and blanch the leaves for 2 minutes.
Once blanched immediately place in iced water to cool.
Put the cod in a rack and cook in the oven for 9 minutes.
Once cooked, turn off the oven and leave the cod in for 5 minutes to rest.
In another pot add a touch of olive oil then add the spring leaves and toss.
Add the seaweed butter and stir to emulsify - adding a touch of water if needed.
Drizzle a little olive oil to finish.
Serve the cod with the spring greens and sprinkle spring onions.