Process ricotta, powdered sugar and vanilla in food processor until smooth. Add citron, peel, and broken up chocolate and process with short bursts just until chopped. Use to fill cannoli shells, garnishing ends with finely chopped almonds or other nuts.
Variations: Fluffy Riccota Filling: Fold in 1 cup heavy cream, beaten until stiff. Pistachio Filling: To either of the above fillings add a few drops of green food coloring to tint pale green. Garnish ends of filled shells with chopped pistachio nuts.