Combine dry ingredients: In a large mixing bowl, whisk together the flour, brown sugar, baking powder, cinnamon, pumpkin pie spice, and salt until well mixed.
Add the cold butter to the bowl. Using a pastry cutter or two forks, cut the butter into the dry mix until it resembles coarse crumbs with some pea-sized pieces.
Turn the dough out onto a lightly floured surface. Gently fold it over itself and shape into an 8-inch circle. Cut into 8 wedges and place on a baking sheet lined with parchment paper.
Whisk together powdered sugar, 2 to 3 teaspoons buttermilk, and 1/2 teaspoon vanilla extract, adding more sugar if too thin. Drizzle over cooled scones.