Preheat the oven to 400°F and line a baking sheet with parchment paper.
In a large bowl, whisk together the flour, sugar, cinnamon, baking powder, baking soda, and salt.
Grate the cold butter directly into the dry ingredients. Toss gently until the butter is evenly coated with flour.
In a separate bowl, whisk together the sourdough starter, pumpkin purée, egg, and vanilla.
Pour the wet ingredients into the dry ingredients and gently mix until a shaggy dough forms. Use your hands to bring the dough together. Avoid overworking it.
For an optional longer ferment: Cover the dough and refrigerate for 6 to 8 hours. Otherwise, continue with the recipe right away.
Place the dough on the prepared baking sheet and gently shape it into a round about 1 inch thick.
Cut the dough into 8 wedges using a sharp knife or bench scraper.
Separate the wedges slightly on the baking sheet.
Bake for 20 to 24 minutes, or until the tops are set and the edges are lightly golden.
Transfer the scones to a wire rack and allow them to cool before glazing.
For the maple glaze, whisk together the powdered sugar, maple syrup, cream, vanilla, and salt until smooth.
If the glaze is too thick, add a tiny splash of cream. If it is too thin, add a little more powdered sugar.
Drizzle the maple glaze over the cooled scones and allow it to set before serving.