(*) For an 18 cm ø cake springform pan or possibly a coated hemispherical baking pan Cook the day before.
Preheat the oven to 160 °C. Grease the baking pan with butter and put it in a cool place.
Mix the eggs with pepper, salt, ricotta, saffron, parsley and parmesan. Cut the spring onions with green tubes into fine rings. Remove the skin from the mackerel fillet, pluck the fillet into pieces and add with spring onions. Pour the mixture into the mold and bake for about 60 min until the mixture is set. Remove from heat, cool and refrigerate until ready to serve.
To serve, turn the frittata out of the mold onto a plate, cut into pieces and bring to the table with bread and perhaps a leafy salad.