Preheat oven to 190C/380F. Grease and lightly flour 3 x 20cm-diameter cake tins.
Place the butter and sugar in a mixing bowl and beat together for 3-5 minutes until pale and creamy. With the mixer still running, add the eggs one at a time, then add the Greek yoghurt and vanilla extract. This is your wet mix.
In a separate bowl, mix together the flour, baking powder, baking soda and ground almonds. This is your dry mix. Add one third of the dry mix into the wet mix and fold in gently. Repeat twice more until the mixture is fully incorporated.
Divide the mixture between the three baking tins and place in the oven for 22-25 minutes until an inserted skewer comes out clean.
Leave the cakes to cool completely in the cake tins on a wire rack.
Take the ice cream out of the freezer and let it soften for 10-15 minutes. Then spoon it out into a large bowl.
Add in three-quarters of the peanut butter. half of the salted caramel and one third of the Nutella. Use a spoon to swirl it all together. Don't overmix though, you want nice swirls in there.
Remove the cakes from the cake tins and place one of the cakes on a serving plate. Spoon on half of the ice cream mixture. Top with the second cake and spoon on the rest of the ice cream mixture.
Top with the third cake. Spread on the remaining Nutella, then spoon on little blobs of the remaining peanut butter and salted caramel. Use a cocktail stick to swirl everything together. Sprinkle on the roasted hazelnuts and chocolate pieces, and either serve immediately (it will be quite soft, so you'll need to serve it quickly), or freeze for 30 minutes. The colder you can get your freezer, the better, as the salt and sugar in the salted caramel will lower the freezing point of the ice cream. slightly.
If it's in the freezer for more than a couple of hours, take it out of the freezer 30 minutes before serving to allow the sponge start to soften again.