Adjusting cooking time and temperature when making smaller portions

I'm perfecting a recipe for queijadas de leite - a traditional Portuguese custard/pastry. It's a mixture of eggs/sugar/milk/flour, very liquid in its raw form. The original instructions call for 30 minutes baking at 350 ºF, and this works quite well when using full sized muffin pans.

I'm trying to adapt it to mini-muffin pans (which are about 1/3 the volume of the full sized), and find that without any modifications they get overdone. Any suggestions on how to adjust the temperature (and perhaps duration) without having to do 10 different batches?

Part of the difficulty is that milk is added at near boiling temperature. If I make lots of batter and try different settings for smaller batches, I'm afraid the cooling of the second, third, etc batches prior to baking will affect the results.