Preheat the oven to 200 °C (fan/convection). Line a large baking sheet with parchment paper.
Sieve together the flour, baking powder, sea salt, and poppy seeds in a large mixing bowl.
420 g plain white flour, 3 teaspoon baking powder, ½ teaspoon fine sea salt, 1 tablespoon poppy seeds
In a separate small bowl, rub together the caster sugar and lemon zest until the mixture becomes fragrant.
100 g caster sugar, Zest of 2 lemons
Whisk the zesty sugar into the flour mixture until well combined.
Add the cold, cubed vegan butter to the flour mixture. Use a pastry cutter or two knives to cut the butter into the flour until no large lumps remain, then rub through with your finger tips. The mixture should resemble coarse crumbs with small, flat pieces of butter throughout. Alternatively, pulse together a few times in a food processor.
120 g vegan butter
In a measuring jug, stir together the vegan yogurt, lemon juice, lemon extract, and vanilla extract.
Pour the wet ingredients into the dry ingredients. Stir together with a fork until a very shaggy scone dough forms. Be careful not to over mix.
Turn the dough out onto a lightly floured surface and pat it into a roughly 20cm (8 inch) disc. Use a sharp knife to slice the disc into 6 even triangles.
If baking later, wrap the sliced disc in plastic wrap or place it in a ziplock bag and freeze for up to a month.
Arrange the scones on the prepared baking sheet, spacing them evenly. Brush the tops with plant milk and sprinkle with Demerara sugar.