Preheat the oven to 180C/350F and line a cupcake tray with liners.
Make the cupcakes first: Place the butter and sugar into a large bowl, or the bowl of your stand mixer and beat until light and fluffy, around 2 minutes on medium-high speed.
Add in the vanilla and eggs, scraping down the sides as necessary, and beat until well incorporated, around 1 minute on medium speed.
Place the flour, baking powder, salt and spices into a medium sized bowl and stir until the spices are evenly dispersed through the flour. Tip into your large bowl and mix on low until the mixture begins to come together, then add the pumpkin purée and continue to mix on low until everything is combined. Turn the speed up to medium for 15-20 seconds just to make sure everything is well mixed.
Divide the batter between the liners, I used a cookie scoop and placed 2tbsp of batter into each liner. Place in the oven for 18-22 minutes, until risen and an inserted skewer into the centre comes out clean.
Place kitchen paper underneath a cooling rack and transfer the cupcakes to the rack as soon as possible. Leave to cool completely.
Once the cupcakes are cooled, place the granulated sugar and cinnamon into a small, shallow bowl and stir until well combined. Take 1/2tbsp of this mixture and place it in another bowl. Leave to one side (this is for sprinkling on top).
To top the cupcakes with sugar: Brush the top of each cupcake with melted butter and then either sprinkle the cinnamon sugar onto each cupcakes, or dip each cupcake into the cinnamon sugar. Leave to one side while you make the frosting.
Place butter, icing sugar and cinnamon into a large bowl, or the bowl of your stand mixer, and mix on low until it starts to come together. Add 1tbsp of milk, then turn the mixer up to medium-high speed and mix until light and fluffy. Add extra milk as necessary, you want your frosting to hold its shape, but be soft enough to pipe. It takes a good 2-3 minutes for my frosting to get ultra light and fluffy, it will pale in colour slightly as well.
Fit a piping bag with an open star nozzle and fill halfway. Pipe a swirl onto the top of each cupcake. Once you've piped all the cupcakes, sprinkle with the cinnamon sugar you took out of your topping mixture.
To finish off the cupcakes, take your Ziploc bag with melted chocolate and make sure the melted chocolate is all in one corner. Snip the corner off of the Ziploc bag, only a small amount, and then drizzle melted chocolate over each cupcake. Leave to set for 10 minutes, then dig in!
Pumpkin Churro Cupcakes will keep in an airtight container, at room temperature, for 5 days. The cinnamon sugar will be absorbed into the cupcake after a few days.