Preheat pizza stone in 450 degree F oven for at least 30 minutes. If not using a pizza stone, use a flat sided or upside-down cookie sheet.
Place the ricotta in a bowl. Add 1 handful sugar and the vanilla and whisk well. While whisking, add in the melted chocolate, little by little.
On a lightly floured pizza peel or board, roll pizza dough out into 2 (12-inch) rounds about 1/4-inch thick. Spoon 1 cup of chocolate filling into center of each round. Plac the remaining chopped chocolate on top. Brush the edges of the dough with beaten egg white and fold each round in 1/2. Fold edges over as you would a piecrust and press to seal completely. Brush off excess flour from dough, brush with more of the egg white and sprinkle with sugar.
Slide chocolate calzone onto preheated pizza stone and bake for 30 minutes or until golden brown.