On a lightly floured surface, roll out the dough to 1/8-inch thickness. With a cutter, cut out rounds 5-inches in diameter. In batches, as necessary, wrap each round onto a cannoli mold, sealing the edges with egg white.
In a deep saute pan, heat the oil to 350 degrees F.
Fry the cannoli in batches until just golden brown and crisp, about 2 minutes. Drain on paper towels, let cool, then gently slip the molds from the cannoli. (Note: Shells can be made 3 days in advance and kept at room temperature in an airtight container.)
Place 1 cannoli shell on a flat surface. Working from either end, fill the cannoli with the ricotta filling (using a pastry bag, if desired), pressing gently to ensure that the middle is filled. Dip both ends in the melted chocolate, then into the pistachios and place on a waxed paper lined baking sheet. Repeat with the remaining cannoli, and serve.