Bring a large pot of water to boil. Scrub the potatoes clean with a sponge. Place the whole potatoes in the boiling water and cook them until they are soft enough to pierce with a fork but aren't falling apart.
Cut the potatoes into 1-inch cubes. Next, slice the fish into similar-sized pieces.
Season both generously with garlic parsley salt.
In the microwave, melt the butter in a small dish (should only take 1 minute). Pour half the melted butter over the potatoes and the other half over the cod.
Lay the potatoes and cod on a baking sheet in one single layer.
Bake it at 425°F for 15 minutes. Then, turn the oven onto a high broil for a few minutes, just until the fish and potatoes develop a nice crust. Serve immediately and enjoy!