Cream the butter and sugar until pale and smooth. Add the lemon verbena and the lemon zest and stir in. Gently and lightly mix in the flour until just incorporated. Don’t overwork it. Roll into a cylinder (about 5cm diameter but it really depends how large you want your shortbread to be), wrap in clingfilm and refrigerate for at least one hour.

Heat the oven to 140C (fan). Line a baking tray with baking paper. Remove the dough and slice into rounds about 1cm thick. Lay the rounds on the tray leaving enough room for the biscuits to spread a little during cooking. Sprinkle them with the granulated sugar and verbena mixture.

Check the biscuits after about 30 minutes. They are ready when the edges are just, but only just, starting to colour. This may take up to 40 minutes depending on your oven.

Remove from the oven. Leave to cool for 5 minutes and then transfer them to a wire rack to cool completely.