  Moir\'e-pattern based potential engineering has become an important way to
explore exotic physics in a variety of two-dimensional condensed matter
systems. While these potentials have induced correlated phenomena in almost all
commonly studied 2D materials, monolayer graphene has remained an exception. We
demonstrate theoretically that a single layer of graphene, when placed between
two bulk boron nitride crystal substrates with the appropriate twist angles can
support a robust topological ultra-flat band emerging from the second hole
band. This is one of the simplest platforms to design and exploit topological
flat bands.
