Method
Heat the oven to 180°C/350°F/gas mark 4. If you’re making your biscuits using a moulded tin, grease it lightly with butter; otherwise line a baking sheet with baking parchment.
Place the egg yolk, salt, vanilla and half of the sugar into a small bowl. Whisk for about 3–4 minutes, until light and thick. In a separate, larger bowl, use a clean whisk to whisk the egg white until it forms stiff peaks. Add the remaining sugar to the white, and whisk again until firm.
Add a tablespoon of the egg whites to the yolk mix, and gently use a rubber spatula to combine fully. Then, add the yolk mix to the remaining egg whites, sieve in the flour and, again using the spatula, gently fold everything together until evenly coloured.
Gently place the mixture into a piping bag, taking care not to knock out the air, and pipe the mixture either into your mould or onto the baking parchment in lines about 10cm (4in) long. Divide the blackcurrants randomly throughout the batters, pressing them down lightly with your fingers, then sprinkle over the thyme. Sprinkle with half the icing sugar, then leave to rest for 5 minutes. Sprinkle over the remaining icing sugar, and immediately place the biscuits in the oven. Bake for 12–15 minutes, until golden and fragrant, then remove from the oven and leave to cool. (If you’ve used a mould, remove the biscuits from it as soon as you take them out of the oven and allow them to cool on a wire rack.) The biscuits will keep for up to 2 days in an airtight container.
