  It is proposed to exploit the decay of the meson ${B}^+ \rightarrow p \pi^+
\pi^+ \bar{\Sigma}_c^{--}$ and of its charge conjugate $B^-$ copiously produced
at LHC to obtain a sample of $\Lambda_c$ baryons through the strong decay
$\Sigma_c \rightarrow \Lambda_c \pi$. The sample thus obtained is not affected
by biases typically introduced by selections that depend on specific decay
modes. Therefore it allows a measurement of the absolute branching fraction for
the decay of the $\Lambda_c$ baryon into $ p K \pi$ or into other observable
final states to be performed in a model independent manner. The accuracy that
can be achieved with this method is discussed and it is shown that it would be
either competitive with or an improvement over current measurements.
