1Heat oven to 350ºF. Unfold pastry sheet; place on lightly floured surface. Roll into 10-inch square. Cut in half; place one half on top of the other. Roll to seal edges. Cut crosswise into 4 equal pieces. Place on ungreased cookie sheet. Bake about 20 minutes or until golden brown.
2Melt butter in 2-quart saucepan over low heat. Cook onions in butter, stirring occasionally, until tender. Stir in flour. Cook, stirring constantly, until mixture is bubbly; remove from heat.
3Gradually stir in milk and whipping cream. Heat to boiling, stirring constantly. Boil and stir 1 minute. Stir in remaining ingredients; heat through.
4Split each pastry horizontally with fork. Spoon crab mixture over bottom halves; top with remaining pastry halves. Garnish with additional parsley if desired.