The pension scheme of the European Union institutions (PSEUI). We’re unable to find a definitive list of all the contributors to the PSEUI scheme but all institutions [1] and most agencies [2] (and here [3]) should be included.
Nevertheless, it is worth checking your previous employer was part of the PSEUI, just in case.
For example the European Investment Bank [4] and the European Central Bank [5] have their own pension funds.