  Aims: The determination of elusive redshifts of bright BL Lac objects
Methods: We use the capabilities of newly available spectrograph X-Shooter at
European Southern Observatory (ESO) Very Large Telescope, that combines high
resolution and a large wavelength range, to obtain UVB to near-IR spectra of BL
Lacs. Results: Our observations of PKS 0048-097 detect three emission lines
that permit to derive a redshift z = 0.635. Moreover, a Mg II absorption system
at z = 0.154 that is associated with a foreground spiral galaxy at 50 Kpc
projected distance is found. Conclusions: The obtained redshift allows us to
comment about the optical beaming factor and the absorption of the high energy
spectrum by the Extragalactic Background Light.
