So this filling…it’s pretty much just like a pastry cream, then? Um, let’s say it’s in the same family, reader Hal. Like pastry cream it’s a stirred custard, not a still custard, even though it’s also baked. The process for making it is identical, however under the hood it’s both leaner and employs a more interesting combination of starches.
Galaktoboureko filling is the only custard I’m aware of that uses finely milled semolina (what we call Durum flour) as a thickener. That’s as much for function as for flavor, for as I mentioned this custard is both cooked and baked.
A high-heat baking at 375 degrees Fahrenheit would destroy a typical egg-thickened custard. The heat would cause the egg proteins to clump together and curdle…end of story. Starch prevents that curdling by getting in between the proteins so they can’t coil together. The result is a custard that isn’t as silky as that in, say, a flan, but one that’s soft and still fairly silky. Especially when it’s suffused with syrup.