Take the Ferrero Rochers out of their wrappers and mash them thoroughly with a fork. Put the crushed chocolates in a large bowl and crumble the cookies on top of them. Add in the Nutella and just over 5 oz of the hazelnuts and mix everything together with a spoon.
Divide the mixture in half between medium-sized bowls lined with clear plastic food wrap. Spread the surface of the mixture flat in each bowl, then press them into the center of both bowls to create a depression in each one. Place the two bowls in the freezer for 1½ hours.
Remove the little bowls from each half and stir the rest of the hazelnuts into the peanut butter. Divide the mixture evenly between the depressions in the two halves of the sphere. Place everything in the freezer again for another 30 minutes.
Put a dollop of dark couverture in the middle of a serving platter. When you place one of the half spheres on top of it, it will hold it in place. Carefully remove the food wrap from both halves and place one of them with its curved side on top of the couverture. Next, using the back of a spoon or a brush, spread couverture all over the flat rim of the lower half in order to 'glue' both halves of the sphere together. Place the other half on top to complete the sphere. Use a brush to apply couverture as a 'sealant' between the two halves.
Cut all the Neopolitan wafers in half crosswise, and coat each piece with couverture on one of the sides with wafer. Stick the pieces to the sphere in rows using the chocolate. It's easier if you start at the bottom. Next, stir the rest of the hazelnuts into the couverture and spread the mixture evenly over your giant ball. To finish, you can garnish the praline with little pieces of hazelnut and hazelnut halves.