Preheat your oven to 180C/160C fan/gas 4 and line a 12-hole muffin tin with large cupcake cases.
Grate your peeled pumpkin flesh using a grater with large holes. Wrap the grated pumpkin tightly in some food-grade muslin (or a clean tea towel) and squeeze out as much of the excess moisture as you can.
In the bowl of your stand mixer, combine your dry ingredients (sugar, flours, bicarbonate of soda and mixed spice) and mix thoroughly.
In a separate jug, whisk your eggs and then add these, the oil and the grated pumpkin to your dry ingredients, mixing by hand until thoroughly combined.
Divide the mixture between your cases and bake at the top of the oven for 25-27 minutes (until the mixture stops ‘singing’). They may need a little longer, if the grated pumpkin remained fairly wet.
Once baked, allow your cupcakes to cool in the tin for five minutes, before transferring to a wire rack to cool completely before icing.
While your cakes are cooling, make your Spice Vanilla Buttercream.
Begin by creaming your butter in the bowl of your stand mixer, fitted with the paddle attachment, until pale and smooth. This may take a while, but the longer you leave it, the better.
Add in the icing sugar, a little at a time, ensuring each addition is fully incorporated before adding the next.
Finally, add the vanilla extract and the spices, and mix through thoroughly.
When your cakes are fully cooled, use a piping bag fitted with a large round tip to pipe a large dome of buttercream onto each cupcake and then decorate with a sprinkle of freshly chopped pecans or walnuts (optional).
Once the buttercream has set, store your cupcakes in an airtight container for up to three days at room temperature.