  We derive a partially gauge fixed Hamiltonian for black hole formation via
real scalar field collapse. The class of models considered includes many
theories of physical interest, including spherically symmetric black holes in
$D$ spacetime dimensions. The boundary and gauge fixing conditions are chosen
to be consistent with generalized Painleve-Gullstrand coordinates, in which the
metric is regular across the black hole future horizon. The resulting
Hamiltonian is remarkably simple and we argue that it provides a good starting
point for studying the quantum dynamics of black hole formation.
