Preheat the oven to 190°C. Place the haddock sides onto a large baking tray and lay the shucked oysters amongst them.
Drizzle a small amount of Guinness® Dublin Porter on top of each oyster and place the tray in the oven for about 10 minutes.
In a large pan on the stove, combine the rest of the Guinness Dublin Porter, cream, samphire, mussels and a decent pinch of salt and steam for around 5 minutes while the fish is cooking. The mussels are cooked when they've all opened up.
To serve, ladle out the mussels onto large platters, then rest the haddock and oysters on top.