Preheat a large skillet with 2. 0 tbsp. (27g / 0.95 oz) of olive oil over medium heat, then add the finely diced shallots and sliced spring onions, sautéing for 5. 0 minutes until soft and fragrant.
Place the 4. 0 mackerel fillets (17. 6 oz / 500g) into the pan skin-side down first to crisp, cooking for 4. 0 minutes total until the flesh is just opaque and the skin is golden.
Pour in 1. 0 cup (240g / 8.5 oz) of heavy cream and sprinkle in 1. 0 tsp. (2g / 0.07 oz) of cumin, 0. 5 tsp. (1g / 0.04 oz) of oregano, and 2. 0 tbsp. (5g / 0.18 oz) of chopped chives directly into the pan.
Simmer the entire mixture for an additional 10. 0 minutes on low heat, allowing the sauce to reduce slightly and the Creamy Mackerel to absorb the herbal aromas.
Remove from heat and serve immediately while the sauce is at its peak creamy consistency, ensuring each fillet is well-coated.
Pat the Fish Dry: Before placing your mackerel in the pan, use a paper towel to pat the skin bone-dry. This ensures you get a crispy texture that contrasts beautifully with the velvet-smooth mackerel in cream sauce.