White fish with caramelized citrus butter & capers

For ➋
2 firm slices of white fish fillet, preferably with skin (choose a firm type, such as halibut)
75 g butter + 1 cube for frying fish
2 tbs capers
1 organic lemon
12 sprigs of fresh oregano
freshly ground black pepper & salt

Preheat the oven to 90 ° C. First fry the fish in a pan that can also be put in the oven. Melt a knob of butter in it over medium to high heat and let it heat up well. Season the fish on both sides with salt and pepper. Bake about 4 m on one side, until you have something of a crust. Make sure that the butter does not burn. Lower the heat if necessary.
Turn the fish over and place about 10 m in the oven. (So ​​you do not cook both, but only on one side.) The fillet should be cooked but still juicy, depending on the size this can take a few minutes longer.*
In a second pan, melt the butter over medium heat. Wait until the butter starts to fizz, stir gently with a wooden spoon and keep stirring occasionally until the butter starts to turn golden brown after 5-10 m and smells like nuts.
In the meantime, cut half of the lemon into fine half slices and remove the seeds. Add to the butter together with the capers and fry for 5 m until the lemon starts to brown very slightly.
Season with a pinch of salt and pepper and mix in the oregano (keep 2 sprigs separate for the finish). Place the fish on plates and spoon over the sauce. Finish with the oregano sprigs and an extra turn of the pepper mill. Add the rest of the lemon in wedges. 
Serve with mashed spinach puree.

*Or bake the fish carefully in a pan.