Preheat the oven to 350 °F. Sift the flour into a large mixing bowl and add the superfine sugar and salt. Add the vanilla paste (or extract, if using) to the bowl along with the butter. Using your fingertips, rub the butter into the dry ingredients. As the mixture begins to come together, use your hand to help it form a dough (alternatively, you could use an electric mixer with the paddle attachment on a low speed to make the dough).

Shape the dough into a ball and flatten it slightly. Roll out on a lightly floured surface to about 1 cm/1/2 inch thick. Cut into 15 oblongs. Lift them with a thin spatula (a wide offset spatula or even a thin fish turner would work nicely here). Place them on a baking sheet lined with baking parchment.

Bake for 15 minutes, then turn the baking sheet around and continue baking for 10 minutes, until the shortbread is golden brown. Remove from the oven and dust with an even coating of granulated sugar. Leave on the baking sheet to cool.

Beat the heavy cream with a hand mixer or standing mixer. Halfway through the whipping process, add 1-2 tbsp. of confectioner's sugar, to taste. Continue whipping until you get soft or stiff peaks, as you prefer. Add about 3 crushed blackberries and 3 leaves basil, torn into small pieces, and swirl through the cream. Pour cream mixture into a pretty bowl and top with extra whole blackberries and torn basil leaves.