Dust is present everywhere in the Universe. Dust absorbs and scatters light dimming the astrophysical sources. Precise measurements of the attenuation dependence with wavelength (extinction curve) have been based in the comparison of spectra from pairs of identical stars suffering different amount of extinction. The study of dust extinction is crucial in Astrophysics and Cosmology for this effect hides stars and galaxies, mistakes their distance and masks their nature. On the other hand, the study of extinction curves in other galaxies is also essential to inform our knowledge about dust Astrophysics. However spectra of individual stars can only be obtained for galaxies in the Local Group and precise measurements of the extinction curve have been available only for this tiny region of the Universe. Here we present an optical and UV extinction curve corresponding to a z=0.83 lens galaxy. It has been obtained by comparing the spectra of two intrinsically identical images of the same lensed quasar which follow different paths through the lens galaxy suffering a different amount of extinction. The extinction curve presents the bump at 2175 Å (usually associated to carbonaceous small grains or large PAH molecules) of moderate strength typical of some low density sight lines in the Milky Way. This extension of the standard pair method to the extra-galactic realm open the study of dust properties out to z=1.