Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).
In a mixer bowl fitted with a paddle attachment, beat butter with sugar until light and fluffy (a few minutes).
Beat in eggs, one at a time, beating well after each addition.
Beat in vanilla and then pumpkin spice.
Whisk together flour, baking powder, baking soda and salt.
Stir dry mixture into wet (butter) mixture alternately with buttermilk, making 3 additions of dry ingredients and 3 of buttermilk.
Using an ice cream scoop or 1/4 cup measurer, scoop batter into a muffin tin lined with cupcake liners.
Bake for approximately 15-20 minutes, until cake tester (toothpicks or skewers work well too), inserted in centre comes out clean.
Let cool in muffin tins for about 5 minutes, then remove and let cool completely before adding icing.