For Puff Pastry Bites: Lay pastry sheet on parchment paper-lined full sheet pan. Cut 2 circles from pastry using a 1-1/2 inch round cutter. Using a 1 inch round cutter, cut a circle in center of half of the rounds, leaving a thin outer ring. Repeat until all pastry is used. Discard any remaining pastry.
Combine egg and water. Brush top of full size round with egg mixture, being careful not to let any drip down the side. Place a ring over it, lining up edges carefully. Brush top of ring with egg mixture. Place sheet in freezer for 15 min. Remove from freezer and brush again with egg mixture.
Bake in preheated 375°F standard oven 15 to 20 min. or until golden brown. Turn oven off and open oven door. Let pastry rest in oven 10 min. to dry out.
For Chocolate Ganache: Place chocolate in bowl. Heat cream and sugar in saucepan on medium heat to simmering, stirring occasionally. Pour hot mixture over chocolate. Let stand 5 min. or until chocolate is melted. Stir gently to completely blend chocolate and cream.
Add butter and stir until butter is completely melted. Let mixture cool to room temperature.
To Assemble: Fill each puff pastry bite with 1 Tbsp. OREO Cookie Pieces. Place in a preheated 350°F standard oven 1 to 2 min. or until heated through.
Remove from oven and top with 1/2 tsp. Chocolate Ganache. Sprinkle with 1/4 tsp. of OREO Base Cake and a dusting of powdered sugar.