Orange & rosemary syrup
Bring the water, sugar, orange zest and rosemary to the boil in a pan, simmer until the sugar has dissolved, leave to cool.
Transfer half of the vodka, lime juice and egg whites to a shaker along with half of the reserved blood orange juice and 2 tbsp of syrup, shake for approx. 15 secs. Add half of the ice cubes, shake for a further 30 secs. Pour through a sieve into two glasses. Repeat the process with the remaining ingredients. Garnish the sour with orange slices and rosemary.