Line a lasagna baking dish with sponge fingers. Top with the whipped cream and spread out evenly. Stud with the strawberries across the top then drizzle with Nutella.
Place on 4 slices of the cake then pour over the chocolate custard and spread in an even layer. Sprinkle with half the hazelnuts. Place 4 more slices of cake on top then spoon over the rest of the Nutella. Spread into a thick even layer then finish off with the remaining hazelnuts and chopped chocolate. Chill for at least 2 hours then slice up and serve.