I applied in-person. The process took 2 months. I interviewed at Junta de Castilla y León (Valladolid) in May 2011
Interview
You need to study the material, since it's not quite an interview but rather a test you need to pass, so, you are fine if you have studied hard enough.
Interview questions [1]
Question 1
Law regarding stuff and also about the European Commission, European Parliament and the rest of the European institutions