Egg white is what makes a sour; don’t let anyone tell you otherwise. The secret to a good sour is the dry shake—that is, shake everything without ice first, in order to get a good emulsification. Here’s more than you probably want to know about eggs in cocktails.
1 ½ oz. Maestro Dobel tequila
1 ½ oz. freshly squeezed grapefruit juice
1 oz. simple syrup
1 egg white
2 dashes mole bitters
2-3 dashes Angostura bitters
Pour all ingredients into a shaker with no ice. Seal and shake for at least a minute. Open and fill with ice. Seal and shake again. Fine strain into a chilled coupe. Garnish with a few angostura bitters.