A festive feud is simmering in Germany over who owns the patent rights for vegan chocolate—and with them, a sweet advantage in a market expected to be worth more than $3 billion by 2030.

Bird & Bird is advising German candy manufacturer Katjes as it battles Swiss and German rivals at Nestlé, Lindt, Sprüngli, Casa Luker, Barry Callebaut, and the Swiss retail cooperative Coop.