Equal parts:

• gin
• Campari
• sweet vermouth

Mix with ice in a lowball.

If you have genever, this is one of the few cocktails where you can sub it in directly for gin, though TheGinisIN recommends "In fact, if you up the Genever and Vermouth in the 1:1:1 ratio to a 2:2:1 you come up with a cocktail that is the sophisticated brother of the Manhattan. The Campari brings a lot of the qualities that the bitters in a Manhattan bring to the table."

Variations:

http://www.esquire.com/food-drink/drinks/a34843/the-new-negronis/

Aging Notes:

Two weeks aging in oak really brings out smooth vanilla notes in the negroni, which unaged can be a sharper cocktail.

I actually like to keep this on constant rotation, topping off as needed (mix ingredients in a measuring cup before transferring to the barrel to avoid imbalance - you might have to drink some remainders)

As I refill, I will occasionally toss in a dash of orange liqueur, bitters, or St. Germain, depending on my mood.