Preheat the oven to 180°C. Mix together the cake flour, wholewheat flour and salt. Rub in the cold butter. Add the milk and egg, bring the pastry together, wrap it in clingfilm and rest it in the fridge for 30 minutes.
Once it has chilled, roll out the pastry between two sheets of cling film and place in a well-greased 30cm tin.
Prick the base with a fork, place a piece of baking paper and baking beans on top, and bake for 15 minutes. Remove the baking paper and baking beans and bake for a further 10 minutes.
Remove from the oven and reduce the temperature to 160°C. Layer the butternut, mushrooms and feta in the tin.
Whisk the eggs, season with sea salt and freshly ground black pepper and pour over the filling. Bake for 1 hour and 30 minutes. Place a piece of tinfoil over the cake and cook for a further 6 to 8 minutes. Serve hot or cold, garnished with crunchy kale chips and drizzled with olive oil.
Cook’s note: The kale chips are from Earthshine, winner of the Eat In DStv Food Network Produce Award for the Best Small Producer: Earth, and the feta from Buffalo Ridge, winner of the Best Small Producer: Dairy/Cheese award.