Preheat the oven to 180°C/160°C fan/350°F/gas mark 4. Line a 23 cm / 9 inch square cake tin with baking parchment, making sure that you leave some overhanging so that you can easily lift the baked bars out of the tin.
Start by making the shortbread. Whisk together the softened vegan butter, caster sugar and vanilla extract with an electric mixer until it is light and fluffy.
Sift together the plain flour and cornflour (cornstarch) then add them to the butter mixture. Stir with a spatula until it forms a dough, it may seem like it is too much flour but it will combine eventually.
Tip the dough into the prepared cake tin and use your hands to pack it down as firmly and as evenly as possible.
Bake the shortbread for 40 mins until it is golden brown. Loosely cover with tin foil towards the end of baking if it starts to colour too much.
Meanwhile make the streusel topping. Mix the flour, brown sugar and cinnamon in a bowl. Rub in the cold butter using your fingertips until no lumps of butter remain and the mixture is clumping together then stir in the chopped pecans.
To make the pumpkin filling, place the pumpkin puree, silken tofu, melted butter, sugar, maple syrup, cornflour, spices, vanilla and salt in a blender and blitz until smooth.
Pour the pumpkin filling over the baked shortbread and spread it level. Scatter over the streusel.
Bake for 40-45 minutes until the filling feels set, it will still be slighty soft in the centre but should not feel too squishy. Loosely cover with tin foil towards the end of baking if the streusel starts to colour too much.
Leave the bars to cool to room temperature then refrigerate for at least 2 hours before slicing into bars. Keep refrigerated for up to 3 days.