To make the pumpkin and sweet potato mash, roughly dice into small pieces then boil until soft enough to press into a mash with a fork. Set aside to cool.

Preheat the oven to 180C/160C Fan/Gas 4. Grease a bundt tin with some oil. Press some pumpkin seeds along the outer rims of the bundt using the pregreased oil to help them stick. Set aside your prepared tin.

Put the pumpkin and sweet potato mash in a large bowl and add the muscadova sugar, flour, sultanas, walnuts (if using), mixed spice, pumpkin seeds and baking powder. Mix lightly with a wooden spoon until roughly combined. 

Add the oil, plant milk, vanilla, and speculoos syrup (if using) and beat together well. If mixture is a little dry add a tad more milk. The mixture should be a thick, but pourable consistency.

Carefully spoon the cake batter into the prepared tin without disturbing the arranged pumpkin seeds, and smooth the surface. Tap on bench a few times to remove any air bubbles. Bake for 50–60 minutes, or until a skewer inserted into the centre of the cake comes out a little moist, but clean.

Leave the cake to cool in the tin for 10 minutes, then carefully turn out onto a wire rack and leave to cool before serving.