  A derivation of the neutrinoless double beta decay rate, specially adapted
for the nuclear structure calculations, is presented. It is shown that the
Fourier-Bessel expansion of the hadronic currents, jointly with the angular
momentum recoupling, leads to very simple final expressions for the nuclear
form factors. This greatly facilitates the theoretical estimate of the half
life. Our approach does not require the closure approximation, which however
can be implemented if desired. The method is exemplified for the $\beta\beta$
decay $^{48}Ca \to ^{48}Ti$, both within the QRPA and a shell-model like model.
