Serve straight up or over ice. The Negroni is a popular Italian cocktail, made of one part gin, one part vermouth rosso (red, semi-sweet), and one part Campari, garnished with orange peel. Let sit for a day or two at room temperature. Refrigerate for at least 5 hours before consuming. It is considered an apéritif.. A traditionally made Negroni is stirred, not shaken, and built over ice … Meanwhile strain through a sieve the alcohol and the lemon mixture, then add the strained mixture with the cooled sugar and water syrup, mix to combine.