In this paper, we present a comprehensive investigation of the epitaxial growth of ${\mathrm{Ba}}_{2}{\mathrm{SiO}}_{4}$ on Si(001), a system in which neither crystal symmetry nor lattice constants match in a simple manner. In addition, it has the potential to become the first crystalline high-$k$ gate dielectric. We combined x-ray photoelectron spectroscopy, low-energy electron diffraction, and aberration-corrected scanning transmission electron microscopy (STEM) in order to optimize the epitaxial growth by molecular beam epitaxy. Our focus was on the formation of a high quality crystalline interface. The films were grown by a co-deposition method that requires no diffusion of Si from the substrate. An annealing temperature of $400{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ turned out to be sufficient to form chemically homogeneous films. However, crystalline films require an annealing step to $670\text{--}690{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ for the formation of the epitaxial interface necessary for breaking Si-O bonds. STEM confirms that the interface is atomically sharp and that a single layer of the silicate is changed to a ($2\ifmmode\times\else\texttimes\fi{}3$) structure at the interface from the ($2\ifmmode\times\else\texttimes\fi{}1.5$) bulk structure. Based on our experimental results, we propose a geometrical model for the epitaxial interface. The growth of films with an understoichiometric Si flux leads to the formation of a near-surface Ba silicide that does not restrict the epitaxial silicate growth.