  Materials hosting flat electronic bands are a central focus of condensed
matter physics as promising venues for novel electronic ground states.
Two-dimensional (2D) geometrically frustrated lattices such as the kagome,
dice, and Lieb lattices are attractive targets in this direction, anticipated
to realize perfectly flat bands. Synthesizing these special structures,
however, poses a formidable challenge, exemplified by the absence of
solid-state materials realizing the dice and Lieb lattices. An alternative
route leverages atomic orbitals to create the characteristic electron hopping
of geometrically frustrated lattices. This strategy promises to expand the list
of candidate materials to simpler structures, but is yet to be demonstrated
experimentally. Here, we report the realization of frustrated hopping in the
van der Waals (vdW) intermetallic Pd$_5$AlI$_2$, emerging from orbital
decoration of a primitive square lattice. Using angle-resolved photoemission
spectroscopy and quantum oscillations measurements, we demonstrate that the
band structure of Pd$_5$AlI$_2$ includes linear Dirac-like bands intersected at
their crossing point by a flat band, essential characteristics of frustrated
hopping in the Lieb and dice lattices. Moreover, Pd$_5$AlI$_2$ is exceptionally
stable, with the unusual bulk band structure and metallicity persisting in
ambient conditions down to the monolayer limit. Our ability to realize an
electronic structure characteristic of geometrically frustrated lattices
establishes orbital decoration of primitive lattices as a new approach towards
electronic structures that remain elusive to prevailing lattice-centric
searches.
