Preheat the oven to 425 degrees F. Line a baking sheet with parchment paper or, if you have it, a pizza stone works well as well. Combine dry ingredients in a large bowl. Cut the butter into the dry mixture until the mixture is crumbly and there are no big chunks of butter.
In a separate bowl, combine the pumpkin, half-and-half and egg. Mix egg mixture into dry ingredients, and form the dough into a ball. Form the dough into a large rectangle 1 inch thick and about three times as long as it is wide. Cut the rectangle into equal thirds so that you have three smaller rectangles remaining. Cut each of the smaller rectangles in an 'X' pattern. This should give you 12 roughly equal scones.
Arrange scones on baking sheet or pre-heated pizza stone. Bake for 14 minutes, or until light brown (times with pizza stone may decrease).
For the Mascarpone Pumpkin Icing:
In a small bowl, combine mascarpone, pumpkin pie spice, pumpkin, vanilla, and salt until smooth. Add powdered sugar. Chill in freezer for about an hour.
Allow scones 30 minutes to cool. While scones are warm but not hot spread the icing on top of scones and allow a few minutes for it to set.