We observe Eris, one of the largest trans-Neptunian objects, in the 300 - 2480 nm range with X-Shooter, the first second-generation instrument for the ESOVery Large Telescope, and compare the newly obtained spectra with those available in the literature. The large spectra coverage and high resolving power ( / ' 5000) of X-Shooter allow us to study absorption features due to CH4 and search for other ices' absorptions. We measure the positions and depth of CH4 absorption features and compare them with those of reflectance of pure methane ice obtained from the optical constants of this ice at 30 K to study shifts in their positions. We do not directly detect absorption bands due to N2 or CO ices in the spectra. Nevertheless, the measured wavelength shifts of the CH4 absorption features points to a dilution of this ice in another one on the surface of Eris and the presence of pure CH4 spatially segregated. The comparison of the centers and shapes of these bands with previous works suggest that the surface is heterogeneous.