  Moir\'e superlattices formed in stacks of two or more 2D crystals with
similar lattice structures have recently become excellent platforms to reveal
new physics in low-dimensional systems. They are, however, highly sensitive to
the angle and lattice constant differences between the associated crystals,
limiting the range of the material choice and the possible moir\'e patterns for
a given 2D crystal. Here, we present a novel approach to realize an atomically
flat substrate with a periodic moir\'e pattern that can induce the moir\'e
potential on the material on top by van der Waals (vdW) interactions, without
suffering from the lattice and angle mismatch. By constructing a twisted hBN
(thBN) moir\'e substrate at an angle of about 1$^\circ$, we show that the
graphene on top, aligned around 15$^\circ$ with the neighboring hBN layers,
exhibits typical transport properties under a hexagonal moir\'e potential,
including multiple satellite Dirac points (DPs), Hofstadter butterfly effect,
and Brown-Zak oscillations. All features point to the existence of the moir\'e
potential in graphene formed by thBN with $\sim$1$^\circ$ twist angle. Further
statistical study shows that the twist from a parallel interface between the
hBN layers is critical to induce the moir\'e potential. Our study demonstrates
that the thBN moir\'e substrate can be used to investigate moir\'e physics in
arbitrary materials without being constrained by their lattice constants.
