Step 1: Preheat fan forced oven to 180⁰C.

Step 2: Spread walnuts in a single layer on a baking tray. Roast in oven for 5 to 10 minutes, or until they appear a shade darker. Allow to cool slightly, then place walnuts inside a tea towel and rub with your hands to remove the skins. Dispose of skins and set walnuts aside.

Step 3: To make the pastry, place the flour and walnuts in a food processor and pulse until very fine. Add the butter and Parmesan cheese and process again until the mixture resembles breadcrumbs. Add the beaten egg and cold water and pulse until the mixture just forms a dough. Wrap the dough in cling wrap and refrigerate for 30 minutes.

Step 4: To make the filling, heat the oil in a large frypan on a medium heat. Cut the bacon into batons and fry for approximately 2 to 3 minutes until crispy and golden. Remove bacon with a slotted spoon onto paper towel to remove excess fat.

Step 5: Remove the cavolo nero stalks then place the leaves in a saucepan of boiling water for 1 to 2 minutes, then drain.

Step 6: Sauté the blanched cavolo in the bacon fat over a medium heat with the finely chopped black garlic until just cooked. Set aside.

Step 7: Grease a 20cm tart tin. Roll out the chilled walnut pastry to a thickness of 2 to 3mm and line the tart tin. Prick the base all over with a fork and return to the fridge for a further 20 minutes.

Step 8: Line the cooled pastry with baking paper and fill with baking beans. Blind bake the pastry for 15 minutes then remove the baking paper and baking beans and return the tart to the oven for a further 10 minutes. Set aside.

Step 9: Reduce the oven temperature to 160⁰C.

Step 10: Lightly beat the whole egg and egg yolks in a medium bowl. Add the cream and whisk to combine. Stir in the bacon, sautéed cavolo nero, gruyere cheese and season with sea salt and freshly ground black pepper.

Step 11: Pour the mixture into the tart case and return to the oven. Bake for 40 to 50 minutes or until the filling is just set. Remove from the oven and leave to cool slightly.

Step 12: Serve warm or alternatively, serve cold for a delicious lunch or picnic.