What's a good pastry dish recipe for the time period of Romeo and Juliet?

Probably an early version of Baklava. A pastry dough made with whole wheat flour and suet would be rolled out and filled with nuts, raisins, and honey. It would be rolled back up and baked over low heat (around 300 degrees) until crisp and golden.

They were very big on tarts and pies back then.

Here is a link of authentic medieval (Romeo and Juliet's time period) recipes that have been translated.

This link is from Europe...where Romeo and Juliet lived...so I can't imagine you will find anything more authentic than this.

http://www.celtnet.org.uk/recipes/mediaeval/breads_cakes.php

dubious has given you a great site, but look up renaissance foods as well. One that is always mentioned is gingerbread, which is easy to make if that's what you need to do.