Quantum materials host a vast array of emergent phenomena, including high-temperature superconductivity, topological properties, and nanoscale charge / spin ordering. One of the challenges is to be able to precisely and deterministically manipulate their properties. Here, we describe how we can dramatically enhance superconductivity in a single monolayer of FeSe through interfacial interactions with a substrate, SrTiO₃. To achieve this enhancement, we employ a combination of molecular beam epitaxy (MBE) and angle-resolved photoemission spectroscopy (ARPES) which provides direct insights into the electronic structure and quantum many-body interactions. The dramatic enhancement of superconductivity in a single monolayer of FeSe / SrTiO₃ remains the largest amongst known superconductors, positioning this system as an ideal platform for investigating fundamental questions about interfacial superconductivity.