Lay the cod filets in a baking dish.
Zest 1 orange and the lemon, then add to the fish.
Squeeze the juice from the orange and lemon and drizzle over the top of the fish.
Add ¼ cup of olive oil to the pan and cover. Let the fish marinate for at least one hour.
Preheat oven to 250°F.
Heat the remaining ¼ cup of olive oil in a large, oven-safe sauté pan.
Carefully shake off excess marinade from the fish and keep it on the side.
Pop the fish into a frying pan and season with salt and pepper.
Cook over medium heat for about 3-4 minutes on each side.
Place the pan into the oven to keep the fish warm while you prepare the sauce.
Melt 2 tbsp of butter in a pan, add in sugar and your leftover marinade.
Slice the remaining orange and add the juice into the pan, then bring it to a boil.
Whisk the sauce until it becomes thick and reduces in volume by about half.
Add about ¼ cup of shredded basil along with the remaining 1 tbsp of butter and whisk until melted.
Pull the fish out of the oven and spoon the thickened sauce over the top.