def METHOD_NAME() -> list[pp.Grid, pp.MortarGrid]:
    """Create a mixed-dimensional grid on a unit square with a single fracture.
    Returns:
        A list containing one subdomain grid (a Cartesian 2x2 grid) and one mortar
        grid (a one dimensional mortar grid with 4 mortar cells).
    """
    mdg, _ = square_with_orthogonal_fractures(
        grid_type="cartesian",
        meshing_args={"cell_size": 0.5},
        fracture_indices=[0],
        size=1.0,
    )
    return [mdg.subdomains()[0], mdg.interfaces()[0]]