dark blue and red gel food colouring
270驳/9戮辞锄 plain flour, plus extra for sprinkling
85g/3oz caster sugar
360驳/12陆辞锄 icing sugar, sieved, plus extra if needed
1 tsp vanilla bean paste (or extract)
180g/6oz salted butter, at room temperature
60驳/2录辞锄 egg white (from approximately 2 free-range eggs), plus extra if needed