To make the sour mix, combine sugar and zest in a medium bowl, using your fingers to rub the zest evenly into the sugar. Pour sugar into a small saucepan along with 1/2 cup water. Bring mixture just to a simmer, stirring to dissolve the sugar. Take the mixture off the heat, and let cool completely. Stir in the blood orange and lemon juice, then strain into a clean jar. Store in the fridge until ready to use (for up to 1 week). You’ll have enough sour mix for 7 to 8 drinks.

To make the cocktail, add vodka, blood orange sour mix and egg white to a shaker with no ice. Cap and shake well to froth the egg white. Add ice and shake again to chill. Double strain into a chilled coupe glass. Let sit for a moment to allow the foam to settle at the surface, then finish with 3 drops of Angostura bitters.