dark blue and red gel food colouring
270²µ/9ΒΎ΄Η³ϊ plain flour, plus extra for sprinkling
85g/3oz caster sugar
360²µ/12Β½΄Η³ϊ icing sugar, sieved, plus extra if needed
1 tsp vanilla bean paste (or extract)
180g/6oz salted butter, at room temperature
60²µ/2ΒΌ΄Η³ϊ egg white (from approximately 2 free-range eggs), plus extra if needed