Final answer:
Shortening is not a traditional ingredient used in concha toppings; instead, ingredients like flour, sugar, and butter are used to create the dough that is baked into the pastries.
Step-by-step explanation:
The concha topping is made with a variety of ingredients that typically include flour, sugar, and butter. The ingredient that is not used in a traditional concha topping from the options provided is shortening. To further understand the process, when baking, the ingredients listed, such as bread flour, eggs, and powdered sugar, are combined with others like butter and vanilla to create a dough. This dough becomes the base for many pastries and in this case, represents the reactants. When baked, they form a delicious product like cookies or conchas, which is the result of these ingredients reacting under heat.