Pre-heat oven to 180 C / 360 F. Prepare a muffin tin with cupcake liners.
Add butter to bowl. Melt for 2 minutes / 60 degrees / speed 2. Check that butter is fully melted. If not, repeat for 1 more minute.
Add sugar, eggs, milk, pumpkin puree, flour, baking powder, pumpkin spice and salt to the bowl. Mix 30 seconds / speed 4.
Use a large cookie/ice cream scoop to divide the mixture into the prepared muffin tin.
Bake in the oven for 20 minutes, or until a knife comes away clean when inserted into the middle of a muffin.
Allow to cool for a couple of minutes in the tin then transfer to a cooling rack to cool completely.
For an extra treat, brush each muffin with a little melted butter and then dip it into some cinnamon sugar (2 tablespoons of caster sugar mixed with ½ teaspoon cinnamon) before serving.