I'm surprised it turned out at all. Cooking syrup to a specific temperature serves to produce a syrup of specific concentration, i.e. ratio of sugar:water. So u

I'm surprised it turned out at all. Cooking syrup to a specific temperature serves to produce a syrup of specific concentration, i.e. ratio of sugar:water. So under-cooked syrup ends up containing a lot more water than desired, as well as not being hot enough to cook and stabilize the egg whites that are presumably in the buttercream recipe.