For Filling: Combine and beat until smooth (about 10 min. With an electric mixer at medium-high speed) Stir in, mixing thoroughly, citron and chocolate pieces Place mixture in refrigerator to chill. For Shells: Sift together first 4 ingredients into a bowl. Cut shortening in with a pastry blender until pieces are size of small peas. Stir in eggs. Blend in, a tablespoon at a time, the vinegar and cold water. Turn dough onto a lightly floured surface and knead until smooth and elastic, about 5 to 8 minutes. Use a small amount of additional flour if necessary to get a smooth dough. Wrap in waxed paper and chill in refrigerator for 30 minutes.

Set out six aluminum cannoli tubes (6 inches long, about 3/4-inch diameter). Set out deep saucepan or automatic deep-fryer. Add vegetable oil (or half vegetable oil and half olive oil) and heat to 360 F. Cut an oval shaped pattern from cardboard (about 6 x 4 1/2 inches). Blanche in boiling water, then cool and finely chop pistachios. Roll chilled dough an lightly floured surface to 1/8 inch thickness. Cut with a pastry cutter and the oval pattern. Wrap dough loosely around tubes slightly overlapping opposite edges. Seal edges by brushing with egg white. Press edges together to seal.

Fry only as many shells as will float uncrowded one layer deep in the hot oil. Fry about 8 minutes or until golden brown, turning occasionally in the oil. Drain over the pan before removing to paper toweling. Cool slightly and remove tubes, then cool completely. Continue forming and frying cannoli shells.

When ready to serve, fill with the chilled ricotta filling. Sprinkle ends with the chopped nuts and dust with confectioners' sugar.