Brown the salmon in a pan with the butter for 1 minute on each side and add a pinch of salt. Meanwhile, cook the rice and the spinach and shape a quenelle. Then put the salmon into an oven dish and place the slices of Provolone Valpadana PDO and pepper over it. Bake at 180 °C for 10 minutes. Garnish with a rosemary sprig and serve.