Edgardo Mortara is a decision available to 
Papal States.
It is visible after 1857 if Papal states is an absolute monarchy and owns Rome (which is the capital of the Papal States). Both requirements are fulfilled at the start of the game. It is possible to take once Papal states have researched idealism.
It gives 15 prestige at the cost of 1 Infamy. It also reduces the relation with every (other) great power with 20.