Funny how my Sous Chef and I were trying to tackle the same thing. After several R&D attempts we came up with this:
1. The vanilla beans will stay suspended in a cooler custard base, no more than 90F.
2. The creaming of the egg yolks and sugar are key as well. The sugar must be fully creamed/dissolved in the eggs before adding the steeped vanilla bean flavored base.
We first scraped the seeds fro the pod and set them aside. Then the pods were combined with the cream, heated to 120F, turned off the heat and allowed to rest on the counter until the temp of the cream was 90F.
In the meantime the eggs, sugar and vanilla beans were creamed together by hand, about 8-10 minutes depending on how conditioned your muscles are 0_0
Strain the flavored cream through a fine mesh strainer into a 4 qt pitcher. Gently incorporate the cream into the creamed egg mix, forming as little as bubbles as possible.
We find that baking the custard in a covered water bath at 300F for 45-50 yields the best results. Make sure your oven is calibrated too. If using a convection oven bring the temp down to 285F.
Hope this helps!