In baked custard the egg acts as thickening agent?

Here's how it works:

* Egg proteins: The proteins in eggs, particularly the albumin, denature (change structure) when heated. This process causes them to solidify and trap the liquid, creating the creamy texture of custard.

* Heat and liquid: When heated, the liquid in the custard mixture (typically milk or cream) heats up, which also helps the egg proteins solidify and thicken the mixture.

So, yes, the egg is the key ingredient that gives baked custard its velvety texture.