Background optical and infrared photon fields can interact with very high-energy (VHE, E > 100 GeV) gamma-rays propagating through the universe.
Absorption patterns induced in the VHE spectra of extragalactic sources can be studied to reconstruct the sum of all optical and infrared emissions from thermal processes dating back to the cosmic dark ages, the extragalactic background light (EBL).
Even though the integrated galaxy light (IGL) is expected to make up the majority of the EBL, recent measurements by the New Horizons mission outside of Pluto's orbit reveal a 4$\sigma$ excess in the optical band with respect to IGL.
To resolve this tension, EBL studies using VHE gamma-rays must transition from an era of discovery to an era of precision.
To reduce the statistical and systematic uncertainties on the measurement of the EBL, we developed a new analysis method using a fully Bayesian framework.
This choice allows us to marginalize over systematic uncertainties of instrumental origin, such as the bias on the energy scale of current-generation VHE observatories.
Using STeVECat, the most comprehensive catalog of VHE spectra to date, we are further able to reduce statistical uncertainties on EBL estimates by more than 30% with respect to previous analyses of archival data.
We provide preliminary constraints on the origin of the New Horizons' excess, which promise an unprecedented precision in gamma-ray cosmology.