Sweet potato & walnut cake

Serves 9

450g sweet potatoes 200ml rapeseed oil, plus extra for greasing 200g plain flour

1 tsp baking powder 245g caster sugar

½ tsp ground cinnamon ½ tsp ground ginger 3 eggs 100g chopped walnuts 75g unsalted butter, softened

150g icing sugar 100g cream cheese ½ tsp vanilla bean paste sea salt

20cm square cake tin baking paper non-stick flat oven tray

Preheat the oven to 170°C/150°C fan/gas mark 3½ and grease and line the cake tin with baking paper. Chop approximately a 5cm cube off one of the sweet potatoes, then peel it and grate onto a plate. Set aside.

Pierce the sweet potatoes with a fork several times, then microwave for 7 mins until soft. Peel the sweet potatoes, then discard the skins and mash the flesh in a bowl. Allow to cool.

In a food processor, whisk together the sweet potato mash, rapeseed oil, plain flour, a pinch of sea salt, the baking powder, caster sugar, cinnamon, ginger, eggs and walnuts until completely combined. Transfer the batter to the prepared cake tin and bake for 40-45 mins until an inserted metal skewer comes out clean. Leave the oven on. Allow the cake to cool, then turn the cake out and remove the baking paper. Place the cake on a chopping board.

Scatter the grated sweet potato onto the oven tray and bake for 5 mins until dried out. Allow to cool on the tray.

In a mixing bowl, whisk together the softened butter with the icing sugar for 2-3 mins until creamy and white. Whisk in the cream cheese and vanilla bean paste until completely combined. Top the cake with the icing and sprinkle over the grated sweet potato. Cut into 9 squares, and serve.