Melt the chocolate in a double boiler.

Whip the ricotta until creamy, then add the melted chocolate.

Beat the egg whites until stiff peaks form. Once firm, gradually add the sugar while continuing to beat.

Using a mixer, blend 1/3 of the egg whites into the chocolate ricotta mixture.

Gently fold in the remaining egg whites with a spoon or spatula.

Spoon the mousse into serving cups and refrigerate for at least 3 hours.