Brown the butter in a hot frying pan, strain through a sieve, and chill in the fridge.
Season hake fillets with salt and refrigerate for 90 minutes to firm the flesh.
Simmer stock in a pan and sauté bacon in the pressure cooker until golden.
Add fennel, onion, garlic, celery, and spaghetti to the pressure cooker and soften for 3 minutes.
Tied herbs, hot stock, and crushed tomatoes to the pressure cooker and cook under pressure for 10 minutes.
Preheat the oven to 160°C.
Whisk the chilled brown butter to a paste and brush onto the salted hake fillets.
Bake the hake fillets on an oven tray for 6 to 8 minutes.
Release pressure, remove herb bundles and tomato skins, then add spring greens and herbs to the hot liquid.
Serve hake over the soup finished with lemon, salt, and olive oil.