We have described a methodology to derive new simulation force fields and an initial application of this infrastructure to create OpenFF 1.0.0 (codenamed Parsley), a SMIRNOFF force field with bonded terms optimized against a range of gas-phase QM reference data. For both training and test sets, Parsley provides more accurate molecular geometries and conformational energetics, while preserving accuracy for a range of condensed phase properties. Importantly, it also yields highly competitive accuracy in calculations of relative protein-ligand binding free energies. This work lays a foundation for efficient iterative force field improvement, which is already underway in subsequent releases (OpenFF 1.1, 1.2, 1.2.1 and 1.3, to be described elsewhere). This work could also be naturally extended to automatically derive molecule-specific (i.e. "bespoke") parameters and we are actively developing software tools for this application.