Preheat the oven to 180 °C.
Finely chop the spinach and put the strips in a bowl. Add the mascarpone and curry paste. Season with salt and pepper. Mix everything through the spinach. This is best done with your bare hands; gently knead the mascarpone and curry paste into the spinach. Put the spinach in an oven dish and place in the preheated oven for 20 minutes.
Fry the fish in the pan with a good amount of butter. When the fish is almost done, add the capers and a generous splash of soy sauce. Let it rise for a while and carefully turn the fish over (see tip), so that the sauce colors the fish nicely all over. Season the fish only with black pepper (soy sauce is already salty).
Remove the baking dish from the oven and arrange the fish on top. Pour the sauce over the fish. Serve.

TIP: in advance
Cod, the favorite fish of many Belgians and Dutch. Choose a thick piece of cod, which you fry briefly but powerfully. You can see how I make the recipe in the cooking video. You can easily make the casserole in advance and keep it in the refrigerator. When the time comes you just put it in the oven for another 20 minutes. I wouldn't bake the fish until the last minute though, but cod doesn't need to bake long, it's at its best when it's still glazy. Alternatively, you can also cook the fish in the oven. Count on about 15 minutes in a hot oven at 180 °C.

TIP: soy sauce
There are many different types of soy sauce. Some are very salty and can mess up your dish. So look for a quality, mild soy sauce. And when you use soy sauce, taste it and don't add extra salt.

TIP: flipping fish
The more brittle the fish, the less you want to flip it during baking, or it risks falling apart. I only flip the fish once.