For the scones: In a medium bowl, combine the sugar, baking powder, pumpkin pie spice, cardamom, coriander and salt. If using roasted pumpkin, add 2 1/4 cups of the flour; if using canned pumpkin puree, add 2 cups of the flour. Cut in the butter using a bowl scraper until the mixture resembles a coarse meal. In a separate bowl, combine the pumpkin, egg, and milk. Make a well in the dry ingredients and pour in the wet mixture. Fold until just combined. (If using roasted pumpkin you may need to add up to 1/4 cup more flour to prevent sticking.)
Turn the dough out onto a floured surface and knead until smooth, 5 to 7 times. Form into a flat disc, about 8 inches wide. Cut the disc like a pie into six pieces and place on a parchment-lined sheet. Bake until golden brown, 12 to 15 minutes. Let cool on the baking sheet.
For the maple glaze: In a medium bowl, stir together the confectioners' sugar, maple syrup and cinnamon. Cover with a damp towel until you are ready to use. Dip the top of each scone in the glaze, letting any excess glaze drip back into the bowl. Place on a cooling rack. Sprinkle with the pearled sugar and let set.
Preheat the oven to 400 degrees F.
Slice the pumpkin in half and scoop out the seeds. Cut the pumpkin into quarters and place on a foil-lined baking sheet. Drizzle with vegetable oil and lightly season with salt. Roast until softened, 35 to 45 minutes. Let cool, then scoop out the flesh and mash until smooth. The pumpkin puree will keep covered in the refrigerator for up to 5 days.