1. Sift the flour in a large mixing bowl.
2. Whisk in cornstarch, salt, caster sugar, baking powder, and ground cinnamon.
3. Add in the margarine and use a pastry cutter or 2 forks or your fingers to rub the butter into the flour mixture until it forms a pea-size crumble.
4. Drizzle the soy milk and vanilla extract over the flour mixture and then mix in with a spoon until a rough dough forms.
5. Add frozen or fresh blueberries and gently knead in the dough.
6. Pour the dough onto a floured kitchen counter, and work with floured hands.
7. The dough will be sticky. If it's too sticky, add a little more flour on top. If it seems too dry, add 1-2 more tablespoons of soy milk.
8. Place the dough onto a large floured piece of parchment paper. Sprinkle flour on top of the dough and press into an 8-inch disc, and with a sharp knife, divide into 8 wedges.
9. Place the parchment paper onto a plate and refrigerate for 15 minutes.
10. Meanwhile, preheat the oven to 200°C.
11. Line a baking sheet with parchment paper.
12. After refrigerating, separate each scone and place them 2-3 inches apart on the prepared baking sheet.
13. Brush the top of the scones with 1-2 tablespoons of soy milk and sprinkle sugar on top (optional).
14. Bake for 20-30 minutes or until golden brown and the edges are dry and hard.
15. Remove from the oven and cool for a few minutes on the baking sheet before transfer to the cooling rack.
16. Store the scones at room temperature for 2 days, wrapped in a towel or in a sealed box.
17. Refrigerate for up to 5 days or freeze in a sealed box. Thaw at room temperature the day before.