Cook the fennel cubes in a little boiling salted water until firm to the bite, quench and drain.
Toast the bread slices until golden brown. Froth the butter with the saffron in a pan, toss the fennel in it over a mild heat for 2-3 minutes, season with plenty of salt + pepper. Spread the fennel on the bread slices, sprinkle with pecorino cheese and grill under the grill for about 1 minute. Sprinkle with the fennel greens and serve immediately.