With the final aim of proving the Majorana nature of neutrinos, the NEXT collaboration searches for the neutrino-less double beta decay (ββ0ν) of 136Xe with a gaseous Time Projection Chamber (TPC). The latest stage within the NEXT programme comprised the NEXT-White detector. It was the first large-scale prototype of a high-pressure Xenon gas electroluminescent TPC, and operated at the LSC from 2016 to 2021 with ~5kg of Xe. In spite of the low amount of 136Xe deployed, it was sufficient to measure its two-neutrino double beta decay (ββ2ν) half-life, thanks to two novel techniques: 1) an iterative deconvolution algorithm that provides highly refined reconstruction of single and double electron tracks, improving the background rejection, and 2) a direct subtraction of the ββ backgrounds, measured with 136Xe-depleted data. Then, two alternative approaches have been exploited for the measurement of the ββ2ν half-life, which strengthens the robustness of the analysis: a background-model-dependent analysis and the direct background-subtraction approach, with little dependence on the model. The latter is particularly interesting, since it can be easily extended to ββ0ν searches in future-generation detectors. A preliminary search in NEXT-White for ββ0ν will also be presented.