Preheat the oven to 400° F. Line a baking sheet with parchment paper or a silicone baking mat.
In a medium mixing bowl, combine the flour, brown sugar, spices, baking powder, baking soda and salt; whisk just to combine. Add the cold butter chunks to the bowl and stir with a fork to combine. Cut the butter into the dry ingredients until the mixture resembles coarse crumbs and the largest butter pieces are no bigger than peas. Mix in the butterscotch chips. In a small bowl or measuring cup, combine the buttermilk, pumpkin puree and vanilla extract. Add the wet ingredients to the bowl with the dry ingredients and stir together gently just until the dough comes together. If necessary, knead a bit with your hands, but be careful not to overwork the dough or you will end up with a tough scone.
Transfer the sticky mass of dough to the prepared baking sheet. Pat the dough into a 8 or 9-inch round. Bake until a toothpick inserted in the center comes out clean, about 22-25 minutes. Allow to cool to room temperature. Slice the dough round into 7 or 8 wedges.
To make the glaze, combine the powdered sugar and spices in a small bowl. Add the milk and whisk to combine, until a thick glaze is formed. (If necessary, add a bit more milk to achieve a consistency good for drizzling the glaze.) Use a whisk to drizzle the glaze over the finished scones (I use a plastic baggie with a tip cut off). Allow the glaze to set before serving.