1) Peel potatoes, wash them, cut them into slices about half a cm thick, transfer them to a saucepan with cold water and cook for 5 minutes from the beginning of boiling. Drain them gently arrange them around the fish and add salt.
2) Rinse the fish under running water and dry it with kitchen paper. Salt it inside and stuff it with the fennel cut into small pieces. Transfer it in a baking tray lined with baking paper.
3) Wash the kumquats, blanch them for 2 minutes in boiling water, drain, let them cool, cut them in half and mix them gently with the potatoes. Season all the ingredients with 5-6 tablespoons of oil, pour the sparkling wine over the fish and bake in a preheated oven at 200 ° for about 45 minutes. Leave rest everything for 5 minutes in the pan and, finally, transfer to a serving dish.