Preheat the oven to 375°F. Line two muffin tins with paper liners and set aside.
In a medium bowl, mix together the flour, baking powder, baking soda, salt, cinnamon, ginger and nutmeg.
In a separate bowl, cream together the butter and granulated sugar until light and fluffy. Add in the pumpkin and milk, and mix until combined.
Slowly add the dry ingredients to the wet ingredients, mixing until fully incorporated.
Scoop the batter evenly into the prepared muffin pans, and bake in the preheated oven for 25-30 minutes, or until a toothpick inserted comes out clean. Allow to cool on wire racks.
While the cupcakes are cooling, beat together the frosting ingredients until smooth. Pipe onto the cooled cupcakes.