Despite the Italian-sounding name, it's a Chilean creation rather than an Italian one, and in Chile it's often made with local parmesan-style cheese rather than imported Parmigiano.
Machas — Chilean surf clams — are served on the half shell, topped with butter, white wine, and grated parmesan, then baked or broiled until bubbling. Stalls and cocinerías at Valparaíso's Caleta Portales fish market serve them by the dozen.