This talk is a case study, in which I use a variant of the vertex operator / transfer matrix method to compute a double dimer partition function related to plane partition enumeration. The problem arises in rank 2 Donaldson-Thomas theory for Calabi-Yau threefolds (joint with Gholampour and Kool). The particular partition function I'm computing has a beautiful product form, in which 3 copies of Macmahon's various generating functions for plane partitions arise explicity - one bijectively, and two as scalar commutators. I expect the method to generalize substantially.