Preheat the oven 350 degrees F. Line a cupcake/muffin pan with paper liners, then set it aside.
In a medium bowl, sift together the flour, cornstarch, baking powder, pumpkin pie spice, cinnamon, and salt. Set the bowl aside.
Beat together the butter and sugar, until creamy. Add in the eggs and beat together until it becomes light and fluffy.
Gradually mix in the flour mixture with the milk, continue mixing for about 30 seconds, then whisk in the pumpkin. Scrape the sides of the bowl if necessary.
Scoop the batter into the prepared liners, filling about ⅔ full, about ¼ cup.
Bake for 18-20 minutes, until the cupcakes spring back when lightly touched.
Remove from oven and place on wire rack to cool.
While cupcakes are cooling make your frosting, in a medium bowl, or using a stand mixer, on medium speed, beat together the cream cheese, butter, milk, and vanilla, until it is smooth and creamy.
Add in the powdered sugar, one cup at a time, until it reaches desired consistency for frosting. (To create rosettes, or other piping designs, you will want the frosting thicker, so it holds the shape.)
After frosting, sprinkle with chopped pecans.