Preheat oven to 190C

Spray or grease a 27cm tart tin and line with sweet shortcrust pastry making sure you don’t stretch the pastry. Spread a cup of crushed walnuts onto the bottom of the pastry and push into the pastry slightly. Place the tart tin in the refrigerator to chill for 15 minutes.

Place the sweet potato flesh into a food processor and pulse until pureed. Add eggs, nutmeg, salt, ginger, cinnamon, 1/2 cup brown sugar, golden syrup, vanilla essence and cream and blend well.

Poor this sweet potato mixture into the chilled tart case and place into the centre of the oven and cook for 20mins. 

Meanwhile combine the flour, sugar and butter for the crumble and rub together until it forms extra large crumbs. Add the 1/2 cup of crushed walnuts and mix through.

Bring the partially cooked tart out of the oven and sprinkle the crumble mixture over the top of the tart. Place back in the oven and cook another 20mins

After the combined cooking time of 40 mins has passed, cover the top of the tart loosely with alfoil preventing the over browning of the pastry and crumble. Continue to cook for a further 20 minutes. You should be able to place a skewer into the centre of the tart and it come out cleanly.

Allow the tart to cool completely and then place in the fridge to set properly.

Serve cold with cream.

Notes:

To make sweet potato flesh, bake two large unpeeled sweet potatoes (approx 95ogms) whole in an oven at 190C for approx 1 hour until the flesh inside is completely soft. Allow to cool completely and then peel off the skin and just keep the flesh.