Fillet your mackerel by cutting the fillets from the carcass unless you've bought fillets or had your fishmonger do it for you. Make sure the scales are removed as well.
Remove the bones from the center of the fillets – for example, with a small pair of pliers.
Sprinkle coarse salt on both sides of the fish and let it sit for about 10 minutes.
Rinse the fish under cold water from a tap to stop the curing process.
Vacuum pack the fillets and place them in your water bath.
I gave my fish 20 minutes at 50 degrees Celsius (122 degrees Fahrenheit),
Take the fillets out of the bag (very carefully) and place them on a clean tea towel and pat them dry.
Heat up a pan (I had it on 12 out of 14 on my stove) and add a large dollop of ghee. If you don't have ghee, use neutral oil and add a dollop of butter once the fish has been on the pan for 10 seconds.
Place your fillets skin side down and fry them until crispy. It takes 1-2 minutes.
The meat side should not be fried. Take them off the pan, pat them dry, and serve immediately. For example, with new Danish potatoes or potato salad.
Bon appétit.