<p>The supermoiré lattice, arising from the interference of multiple moiré patterns, reshapes the electronic band structure of the material that hosts it by introducing new mini bands and modifying the band dispersion. Concurrently, strong electronic interactions within the flat bands induced by the moiré pattern lead to the emergence of various correlated states. However, the impact of the supermoiré lattice on the flat band system with strong interactions remains largely unexplored. Here we report the existence of the supermoiré lattice in twisted trilayer graphene with broken mirror symmetry and elucidate its role in generating mini flat bands and mini Dirac bands. We demonstrate interaction-induced symmetry-broken phases in the supermoiré mini flat bands alongside a cascade of superconductor–insulator transitions enabled by the supermoiré lattice. Our work shows that robust superconductivity can exist in twisted trilayer graphene with broken mirror symmetry and underscores the importance of the supermoiré lattice as an additional degree of freedom for tuning the electronic properties in twisted multilayer systems. It also sheds light on the correlated quantum phases such as superconductivity in the original moiré flat bands, and highlights the potential of using the supermoiré lattice to design and simulate quantum phases.</p>