Place the walnuts on a baking tray and toast for 5 minutes, or until starting to brown and smell nutty. Set aside to cool
In the bowl of a stand mixer with the paddle attachment (or with electric beaters), cream the butter and sugar until very pale and creamy, around 5 minutes. Add the eggs, one at a time, beating well between each addition.
Add the ground walnuts, flour, baking soda and salt and fold together until just combined.
Divide evenly between the two prepared baking tins. Arranged the sliced nectarine and blueberries over the batter - no need to press them in.
Bake for 30-35 minutes, rotating in the oven if need be halfway through, until a skewer inserted comes out clean and the top just bounces back when touched.
To make the frosting, beat the butter until pale and creamy, about 5 minutes. Add the icing sugar and beat on low to fully combine. Increasing the speed to medium, gradually add the cream cheese, a small cube at a time, until fully combined. Add the vanilla and passionfruit pulp and fold in to just combine.
Serve in the next hour or two.If not serving immediately or to store leftovers, store in an airtight container in the fridge.