Answer:
A cupcake is not a naturally-occurring substance, with a specific chemical composition and crystal structure; Therefore, it is not a mineral. Its natural ingredients are minerals, though.
Refer to the dictionary definition of a mineral below:
Definition of Mineral
-any of a class of substances occurring in nature, usually comprising inorganic substances, as quartz or feldspar, of definite chemical composition and usually of definite crystal structure, but sometimes also including rocks formed by these substances as well as certain natural products of organic origin, as asphalt or coal.
-Dictionary.com
Actually- In accordance with the above definition-
Most of the ingredients in a cupcake are not minerals either- They are not "naturally occurring" nor do most of them follow the definition of a mineral.
Eggs, sugar, milk, flour, yeast... none of these are minerals
.