Nemesis cake - came out very runny

This particular recipe is one which is so unpredictable, and you are not alone in getting the cow pat result. I think part of the problem lies in the sugar syrup, which is adding water to something that lacks anything to absorb it. So that excess liquid has to evaporate in the baking, and that is being done while it bakes in a bain marie. So your oven is really humid while this is all going on. It also uses whole eggs, which also contain water. To help counter this, I've opted for a slight variation. I whip all the sugar with the eggs, until it forms a thick ribbon- which means you now all the sugar has been dissolved. That is the point of making the syrup, really. Then you don't have to risk a collapse later on, by pouring syrup in. I also make certain to bake a little longer than is called for, until it is nearly set in the center, similar to how you would gauge a cheesecake. The family finds it just as tasty, and honestly I haven't noticed any difference in texture. To be honest, I don't like the recipe as it is written because it has such a high failure rate. I've found other versions which are more dependable, and that I prefer to use for that reason.

Have you checked your oven temperature? Even new ones can be way off, and this is a pretty unusual temperature range. I think that there are probably better ways that this could be baked, but this method did work for me and I never got around to any experiments. The ingredients and method are so simple that it's hard to see where you could go off, short of ancient eggs.