Blackthorn (English)

1½ oz Plymouth Gin
¾ oz Plymouth Sloe Gin
¾ oz Carpano Antica Sweet Vermouth
2 dashes orange bitters
an orange peel for garnish

Stir with ice and strain into a chilled coupe. Garnish with an orange twist.

Similar
Astoria Bianco (+dry vermouth; -sloe gin, sweet vermouth), Martinez (variation 1) (+citrus liqueur; -sloe gin), Martinez (variation 2) (+maraschino liqueur; -sloe gin), Negroni (+Campari; -sloe gin, bitters)
Credit
The PDT Cocktail Book