To prepare the pumpkin, place cubed pumpkin into a shallow, heatproof microwave-safe dish. Cover and steam for 4-5 minutes until tender. Allow to cool slightly and mash with a fork until smooth.
Place the mashed pumpkin into a saucepan and heat it on medium heat for 5 minutes, stirring continuously. (This helps to remove any excess moisture). Set aside and allow to cool completely before using.
Combine flour, baking soda, sugar, butter and pumpkin pie spice in a food processor and pulse to combine. The mixture should resemble coarse breadcrumbs. Place the mixture into a large bowl. Alternatively, you can do this step manually using a pastry cutter.
In a separate bowl, combine the pumpkin, yogurt, egg and vanilla.
Add the wet ingredients to the dry ingredients and stir until the mixture comes together. (see note 3)
Place the pumpkin scone dough onto a prepared baking sheet (lined with parchment paper) and shape it into a disc.
Cut the dough into eight even triangles and place them in the refrigerator while your oven heats up. (see note 5 & 6)
Preheat your oven to 200 deg C (400 F) and bake for 20 minutes until golden brown. Drizzle the glaze when scones have cooled.
Combine the powdered sugar and milk to form a thick paste and drizzle over cooled scones.