According to the current models of galaxy evolution in a hierarchical cosmology, low mass Black Holes (<10^7 Msun) at low redshift contain clues about the formation of the first Black Holes and Galaxies. Moreover, as they extend the dynamic range of the BH-mass/galaxy scaling relations to extreme values, they are very useful in constraining the AGN/Galaxy co-evolutionary models. In the past years, in the framework of the verification of the AGN unified model, there have been several attempts to detect faint broad emission lines in type 2 AGN with both NIR and polarised spectroscopy. We here present the new results from a systematic study performed using deep NIR (VLT and LBT) spectroscopy of a sample of about 40 AGN2, drawn from the complete SWIFT/BAT 70-month hard (14-195 keV) X-ray selected sample. A new virial relation able to measure the BH mass using the broad component of the Paschen Beta line will be presented. Thanks to the above relation we have been able to directly measure, when the BLR has been detected, the BH mass of type 2 AGNs. The implications on the measure of the local Intermediate BH Mass Function will be discussed.