What is the secret to avoid bitter-tasting rapini?
To get the best out of rapini, you need to blanch it first. Use well-salted water. Detach the thickest stems from the leaves (these can be peeled and used).  Add to boiling water and cook for 3 to 4 minutes. Remove from the water and chill (if using later), or add to a pan with plenty of olive oil and garlic to finish cooking. Remember, though, that bitterness is a characteristic of this vegetable, so you will not completely eliminate it.