Preheat the oven to 350°F (180°C) and line a standard cupcake pan with 12 cupcake liners.

In a large bowl, cream together the softened butter and sugar with an electric mixer for 1-2 minutes until fluffy.

Add the egg, egg yolk, and vanilla extract, mixing until pale and smooth, about 1 minute.

Mix in the milk, sour cream, and pumpkin puree until well combined.

In a separate bowl, whisk together the sifted flour, cocoa powder, pumpkin pie spice, baking powder, baking soda, and salt.

Combine the dry ingredients with the wet ingredients, mixing until smooth.

Divide the batter evenly among the cupcake liners, filling them about 3/4 full.

Bake for 17-19 minutes or until a toothpick inserted in the center comes out clean.

Allow the cupcakes to cool in the pan for 5 minutes before transferring them to a cooling rack to cool completely.

Dry the canned pumpkin puree by spreading it on a plate and dabbing with paper towels until it measures 1/4 cup (45g).

In a medium bowl, beat the softened butter until pale and fluffy, about 5-10 minutes.

Add the cold cream cheese and mix until combined.

Incorporate the dried pumpkin and pumpkin pie spice, then add the powdered sugar gradually, mixing until light and fluffy.

Transfer the frosting to a piping bag fitted with a decorative tip.

Once the cupcakes are completely cooled, pipe a generous amount of frosting onto each.

Serve and store any leftovers in an airtight container in the fridge for up to three days.