The STC holder must make the application via the FAA Aircraft Certification Office (ACO) that did the original approval. The ACO must provide a covering letter endorsing and classifying the application (Basic or non-Basic) and forward it to EASA. Applications where EASA agrees the classification as 'Basic' are normally dealt with quickly. Please note that FAA STCs that apply to a number of different aircraft types as referred to in the 'Applicable Model List' (AML) will generally not be accepted by EASA.
unless split into different applications, one per Type Certificate. This split may be done at EASA if not done by the applicant but will effectively be treated as multiple applications. If in doubt, please contact EASA.