In a small bowl, mix the miso paste, mirin, soy sauce, and sugar until smooth. Make sure there are no lumps so the glaze coats the fish evenly. This mixture will give the cod its signature flavor.
Place the cod fillets in the glaze and coat them well on all sides. Let them sit for about 10–15 minutes to absorb the flavors. Avoid marinating too long, as miso can overpower the fish.
Bring a saucepan of salted water to a boil and add the cauliflower florets. Cook until they are very soft and tender, which usually takes about 10–12 minutes. This ensures a silky smooth puree later.
Drain the cauliflower and transfer it to a blender. Add butter, cream, garlic, salt, and pepper, then blend until smooth and creamy. If needed, adjust seasoning to taste.
Heat olive oil in a frying pan over medium heat. Place the cod fillets in the pan and cook for about 3–4 minutes on each side. The glaze should caramelize slightly while the fish becomes flaky.
Spoon the cauliflower puree onto a plate and gently place the cod on top. Make sure to drizzle any remaining glaze from the pan over the fish. Serve immediately for the best taste.