Neutrino fluxes are currently affected by large normalization uncertainties (5-10%). Neutrino physics will require measurements of absolute neutrino cross sections at the GeV scale with exquisite (1%) precision in the near future. For this reason a reduction of the present uncertainties by one order of magnitude would be highly beneficial. This goal might be achieved by producing a sign and momentum selected narrow band beam and monitoring the production of $e^{+}$ in the decay tunnel from the decays of charged Kaons ($K_{e3}$ channel). This technique, which requires a special instrumented beam-line, would allow a 1% level measurement of the cross-sections of the neutrino species ($\nu_e$ and $\bar{\nu}_e$) which are the final states involved in the searches for CP violation with muon neutrino beams at long-baseline. The ENUBET Horizon-2020 ERC Consolidator Grant, approved by the European Research Council in 2015, is the framework within which such a non conventional beam-line will be developed. We present a progress report of the project (2016-2021) after about one year of work, the experimental results on ultra-compact calorimeters suited for the instrumenting the decay tunnel and the R&D in the design of the hadronic beamline.