Yes, pastry cream has a lot. Two and a quarter ounces in this recipe, which is a ton when you consider that pie fillings have maybe a tablespoon. Is it really necessary? It is if you plan on using the pastry cream for a thing like a Napoleon, in which case the pastry cream is a structural element. In the case of an éclair you can cut back on the cornstarch if you wish, since it won’t be holding anything up (I still like a thick texture). Interesting isn’t it, that in the world of pastry cake, crust and filling recipes vary according to their role as building material. It’s why people often compare the pastry arts to architecture, and possibly why there are so many architecture school grads working in pastry and vice-vera. OK maybe not vice-versa, but it could happen. Why not?