Combine in an old-fashioned glass over ice. Garnish with the lemon peel. Originally this drink was served without ice, but these days you won't find many takers for warm gin.
One of the classic drinks I used to serve at the Hotel Bel-Air was Pink Gin, which called for orange bitters. After going through two or three bottles of DeKuyper Orange Bitters, I spoke to the steward about ordering more. He informed me that it was no longer produced, and had not been available for over twenty years. There are now a few compatible products available: The Fee Brothers in Rochester, New York, produce an orange bitters, but it lacks the flavor and punch of the original. A better one is produced in Europe by the Bols Company, but sadly it is not available here.