Preheat oven to 400°F.
For the crust, add the water and butter to a medium saucepan and bring to a boil over medium-high heat. Add the flour all at once and stir constantly over heat until a smooth ball forms. Remove the saucepan from the heat. Use a spoon to break the ball into pieces to release steam and aid cooling. Let cool 5 minutes.
Add eggs, one at a time, beating well with an electric mixer after each addition. The finished pastry should have the appearance of buttery mashed potatoes. Spread the pastry into a greased 13x9 inch glass baking dish. Bake 25 minutes or until well puffed and golden. Allow the crust to cool in the pan completely.
For the fillings, in the bowl of an electric mixer, beat the cream cheese, milk and pudding mixes together in a large bowl until smooth. The mixture will be thick. Spread the filling over the crust in the dish. Beat the heavy cream and vanilla extract in a separate chilled bowl until stiff peaks form. Spread the whipped cream over the filling and chill for 25 minutes.
For the ganache, combine the chips, heavy cream and butter in a microwave-safe bowl. Heat at 30 second intervals until melted (about 1 minute total). Let stand for 1 minute and then whisk together. Let cool slightly. Use a spoon to drizzle the chocolate ganache over the cake, or use a pastry bag with the end snipped to pipe on the ganache. Sprinkle the cake with the chopped nuts. Serve chilled with maraschino cherries on the side, if desired.