  We provide a direct proof of two-electron Andreev transitions in a
superconductor - normal metal tunnel junction by detecting them in a real-time
electron counting experiment. Our results are consistent with ballistic Andreev
transport with an order of magnitude higher rate than expected for a uniform
barrier, suggesting that only part of the interface is effectively contributing
to the transport. These findings are quantitatively supported by our direct
current measurements in single-electron transistors with similar tunnel
barriers.
