2 oz. base spirit
1 oz. fresh lemon juice
1 heaping bar spoon, or scant 1 tablespoon, of marmalade (citrus flavors like orange and lemon work best)
¾ oz. egg white
Lemon peel, for garnish
Add first four ingredients to a cocktail shaker without ice, and shake vigorously. Add ice, and shake vigorously again. Double strain into a chilled cocktail glass, and garnish with a lemon peel.
Note: Baird and Harris also make a gin and elderflower variation of this sour by using 1.5 oz. of Plymouth gin, ½ oz. St. Germain, 1 oz. lemon juice and a heaping bar spoon of lemon marmalade.