[tropo]

I suspect the butter is the result of two substitutions. This has happened to many recipes.

First, there was a money-saving switch from lard to commercial shortening or margarine. Either one was made of partially hydrogenated vegetable oil.

Second, due to trans fats or a desire to be less fake, that got switched to butter.

Lard makes wonderful brownies. Compared to butter, the taste comes out far cleaner. The purity of the chocolate really comes through.

Another fine option is coconut oil.