  We formulate a notion of $E_{-1}$ quantisation of $(-2)$-shifted Poisson
structures on derived algebraic stacks, depending on a flat right connection on
the structure sheaf, as solutions of a quantum master equation. We then
parametrise $E_{-1}$ quantisations of $(-2)$-shifted symplectic structures by
constructing a map to power series in de Rham cohomology. For derived schemes,
we show that these quantisations give rise to classes in Borel--Moore homology,
and for a large class of examples we show that the classes are closely related
to Borisov--Joyce invariants.
