Bomb one of their airbases. Russia can annex Crimea with no real response, so why should the EU show restraint? (I am not suggesting a bombing campaign, just a targeted strike on the airbase from which the intercepting fighter jet departed.) What’s Russia going to do? They want that Nord Stream pipeline. They aren’t going to militarily respond over some two bit dictator, even one friendly to Russia. The Nord Stream energy revenue is probably going to be much higher than the entire Belorussian economy.