Rinse the sweetbreads in cold water. Blot them in a towel and, by hand, remove the "naves" and the skin, avoiding splitting them.
Dip the asparagus tips in a pan of salted boiling water. Cook them 7 minutes, so that they stay crunchy. Drain and reserve.
Heat 15 g of butter in a casserole. Brown the rice for 2 to 3 minutes over medium heat. Wet with muscat. Cover and cook on low heat 4 to 5 minutes. Add pepper and myrtle. Cook for 2 minutes. Bind the juice with the remaining butter. Add the asparagus.
Present the sweetbreads in the casserole sprinkled with chervil leaves.