Cut the butter into cubes and pop it in the freezer while preparing the rest of the ingredients.
In a large bowl, stir together the flour, brown sugar, baking powder, pumpkin pie spice, cinnamon, and salt.
In a smaller bowl, whisk the egg with the pumpkin puree, sourdough starter, heavy cream, and vanilla.
Using a pastry blender, cut the frozen butter into the dry mixture until it resembles small pea-sized crumbs.
Pour the wet ingredients into the dry. Start mixing with a spoon, then gently knead with your hands just until it forms a ball. Don’t overmix—it should look a little rough and shaggy.
Place the dough on your work surface and shape it into a round disc about 1 inch (2.5 cm) thick. Cut into eight wedges using a knife.
Preheat the oven to 400°F (200°C). While it heats, refrigerate the scones for 10–15 minutes. Line your baking sheet with parchment paper.
When ready, place the chilled scones on the baking sheet, spaced apart. A bench scraper makes transferring easy.
Bake for 20–25 minutes until golden. Let them cool on a wire rack.
While cooling, whisk together all glaze ingredients in a small bowl.
Drizzle the glaze over the cooled scones.