The IRS raspberry cocktail.

The numbers are in. Zola—the restaurant in DC’s International Spy Museum—sold 26,000 martini glasses of its trademark beverage last year. The white-cranberry cosmopolitan has become a staple of Zola’s regular crowd—so much so that when Ralph Rosenberg, director of operations for Zola and four other DC eateries, removed the drink—his own invention—from the menu, he received a number of complaints.

“I don’t even like cocktails,” says Rosenberg as he slips behind the bar toting a dish of fresh raspberries. “I’m more of a vodka-and-Sprite kind of guy.”

A New Yorker with 30 years of restaurant experience and a Culinary Institute of America grad, Rosenberg is the mind behind Zola’s “dessert drinks” bar menu. His latest effort: an IRS raspberry cocktail in honor of the April 15 tax deadline.

With each new day of note—or simply when the bar menu needs something fun or new—Rosenberg heads to the kitchen to concoct an themed cocktail. His last was the Love Potion Z, a Valentine’s Day-inspired red jewel containing Turi Estonia vodka, Cruzan mango rum, Cointreau, ginseng, and wild-cherry juice. Rosenberg says the drink had customers, mostly women, flagging down waiters to ask what colorful cocktail had just passed them by. Love Potion Z’s popularity may make it a menu staple, says Rosenberg.

His goal in crafting the rotating cocktail menu is to seek out and import new ingredients that no one else in the business has. He’s brought in black vodka, which had businessmen downing the Black Tie Bawl. Rosenberg claims to be the first to put white-cranberry juice on the menu when the product emerged on the market about six years ago. Now, for the IRS drink, Rosenberg is buying up Steaz raspberry-and-green-tea soda to bring together colors and flavors in his playful, stick-it-to-the-man cocktail.

The IRS cocktail is served in a plain 14-ounce bar glass, and its primary liquor is bourbon. He says that when he introduced the drink to his staff, they were hesitant to try it because of the bourbon, but all were pleasantly surprised.

The two ounces of Maker’s Mark bourbon add to the flavors of the raspberry-and-green-tea soda and muddled fresh mint and lime. A splash of white-cranberry juice tops off the cocktail’s summery flavor and adds a light-yellow, bejeweled crown to the soda’s light-pink hue. Rosenberg slides five fresh raspberries onto a skewer to top it all off.

He says it doesn’t take him long to think up cocktails such as his popular Jade, a green Grand Marnier-based drink that baffles sippers at its simplicity of ingredients. He also likes to keep the steps required for making a cocktail down to two or three. While Zola has won numerous awards including “best bar scene” in 2004 from the Restaurant Association Metropolitan Washington, Rosenberg says he’s ready to try out a whole new beverage program. His first move will be to come up with a way to craft cocktails tableside so that guests can see how they’re made.

The IRS drink may be a test subject for this new tableside ritual, says Rosenberg, especially if it becomes a crowd favorite. The bourbon, however, may hold it back—the drink might be more appealing to female customers with a smooth vodka or gin. But those who give it a try will find the typical bourbon punch—in this drink, with these flavors—less than taxing.