I am making the wedding cake for my cousin's wedding. My daughter is also in the wedding party. So it is a busy couple of day.

Due to timing (decorating time, travel, rehearsal etc.) the cake will need to sit overnight plus out at the hall. (so over 24 hours at least). I have a moist cake and buttercream that will be fine but I have never done a vanilla custard before so I need a recipe that will not go bad in that time. Please help!!!

You might want to consider purchasing a sleeve of Bavarian cream filling, which has preservatives that would allow it to sit safely at room temperature for that long. I do not believe that any homemade custard would be able to meet your requirements.

FYI some of the sleeved Bavarian "cream" contain no dairy products, only shortening, sugar, starch, water and white titanium dioxide.

If you use nondairy creamer mixed with water and instant pudding mix, you will have an edible food substance that might not go bad before the cake is eaten.

Any recipe with milk, cream MUST be kept refrigerated or your cousin's wedding will be memorable for the large number of trips to the hospital.

Well I guess you would start by reading the label on the pudding mix.

Instant pudding mix that I buy lists on its label sugar, starch, and other stuff but no mention of dry milk powder...when mixed with water it produces a clear starch gel that is shelf stable unless it starts fermenting.

Even if your brand contains no milk powder, non-dairy creamer (liquid) requires refrigeration just as milk does. http://www.coffee-mate.com/Faqs.aspx

I would just hesitate to make that concoction and cross my fingers that it's shelf stable.

lol ok, no custard. Thanks everyone

The non dairy Bavarian Cream from the sleeves are quite tasty.