Boil the potato cubes in salted water until par-cooked, about 8 minutes.
Drain the potatoes thoroughly and pat them dry.
Heat 2 tablespoons of olive oil in a large skillet over medium-high heat.
Sauté the potatoes until they achieve a deep golden brown crust, then remove and set aside.
Season the cod fillets generously with salt and pepper.
Add the remaining oil to the same skillet and sear the cod for 3 to 4 minutes per side until opaque.
Remove the fish and set aside, keeping warm.
In the same skillet, add the garlic and rosemary, sautéing until fragrant.
Pour in the vegetable broth to deglaze the pan and reduce by half.
Stir in the heavy cream and simmer until slightly thickened.
Return the potatoes and cod to the pan briefly to coat in the sauce before serving.