More than a few custard recipes call for the addition of a starch, usually corn starch, as a stop-gap against curdling. You frequently find it in pie recipes, flourless chocolate cakes recipes (which routinely instruct home cooks to bake them for extended periods at higher-than-ideal temperatures), and in custard filling recipes, especially pastry cream.
How does starch protect against curdling? Well if you remember previous posts on bread baking and/or starch gels, you’ll recall that heat and moisture have a way of “unbundling” individual starch (carbohydrate) molecules from starch granules like pieces of hay off a hay bale. Inside a heating custard, those starch molecules get between the coagulating proteins, preventing them from bonding to tightly to one another and preserving the delicate lattice. They also absorb some of the oven’s heat, preventing the proteins from getting too hot to begin with.
The up side is that you get a nigh-indestructible custard as long as you don’t get totally nuts with heat. The down side is that then end product frequently tastes starchy, and isn’t nearly as silky and elegant as the custard made without.