  We present the results of the application of the unitarity-based Dispersion
Matrix approach to semileptonic charged-current $B$ decays. This method allows
to achieve a non-perturbative and completely model-independent determination of
the hadronic form factors. Starting from lattice results available at large
values of the momentum transfer, the behaviour of the form factors in their
whole kinematical range is obtained without introducing any explicit
parameterization of their momentum dependence. We will focus on the analysis of
Lepton Flavour Universality by computing the $\tau/\mu$ ratios of the branching
fractions of the $B \to D^{(*)} \ell \nu$ and $B \to \pi \ell \nu$ decays. The
most important result is that, for the first time, the discrepancies between
the SM expectation values and the measurements of the Lepton Flavour
Universality ratios for the $B \to D^{(*)} \ell \nu$ decays are reduced at the
1.3$\sigma$ level for each of the two channels, separately.
