1. Pre-heat the oven to 180c/gas 6 and line a couple of baking trays with greaseproof paper/silicone baking sheet.

2. With an electric mixer or by hand, put the butter and sugar in a mixing bowl and beat until light and quite fluffy.

3. Mix in the egg yolk and lemon zest, then add the flour and raisins/currants. Add a splash of milk and mix until it comes together as a soft dough.

4. Flour a surface or board and knead the dough lightly for a minute. Roll out to about 0.5cm thick and cut out circles of 5/6cm before placing on the baking tray.

6. Bake for around 10 minutes depending on the fierceness of your oven - keep an eye on them. While they’re baking, beat the egg white in a small bowl.

7. Remove the biscuits and brush with the egg white. Sprinkle over a little caster sugar and return to the oven for another 5 to 7 minutes - they should be golden and not starting to brown at the edges.

8. Leave to cool on the trays for five minutes, then move to a wire rack to cool completely.