The ring traveled about 87 mph in a container of ice cream through a pneumatic tube, before Kouka discovered it a couple bites in.
Labusche then got down on one knee and Kouka accepted the proposal as a group performed Toto's "Africa."
"Out of nowhere my favorite song came on and this delicious dessert arrives and then there's a ring," Kouka told Stuff. "I was trying to act cool but really I had crazy butterflies."
The couple have been dating for two years and Laubsche decided to propose six months ago. He said the proposal took a good amount of planning, but added that he feared she would be suspicious.
"The most stressful thing about it though was just making sure she turned up," he said. "I was convinced she must have known something was up because I just kept banging on about how she couldn't forget we were going out for dinner."
Kouka admitted that she had some idea what was going on, but stopped anticipating a proposal after they had been at the cafe for about an hour.
The couple plan to get married in October after the viral proposal.
"Just to confirm, romance is not dead," Kouka said.
