Preheat the oven to 200°C (400°F).
Steam cauliflower florets for 12-15 minutes until very tender. Drain thoroughly and pat dry with a clean towel to remove excess moisture.
Mash the cauliflower with 50g butter and 75g of the shredded cheddar cheese until smooth; season with salt and pepper and set aside.
In a large skillet or saucepan over medium heat, combine the heavy whipping cream, cream cheese, Dijon mustard, nutmeg, and lemon zest. Whisk continuously until the mixture reaches a gentle simmer and starts to thicken (approximately 5 minutes).
Add the cod, salmon, smoked haddock, and prawns to the sauce. Stir gently to coat and simmer for 3 minutes until the fish is opaque but not fully cooked.
Fold in the fresh parsley and dill. Taste and adjust seasoning with salt and pepper.
Pour the seafood and sauce mixture into a 2-quart (approx. 20cm x 20cm) ovenproof baking dish.
Arrange the quartered hard-boiled eggs evenly across the top of the seafood mixture.
Spread the cauliflower mash over the top of the dish, using a fork to create textured ridges.
Sprinkle the remaining 75g of shredded cheddar cheese over the mash.
Bake for 20-25 minutes until the topping is golden brown and the cream sauce is bubbling at the edges.
Allow the pie to rest for 5 minutes before serving to let the sauce set.