The name “brownies” first appeared in the 1896 Boston Cooking School Cookbook, where it describes molasses cakes baked in small tins.

The first known recipe for brownies was published in the 1897
Sears, Roebuck Catalogue. The origin of the Brownie is thought to be
American. It is classified as a bar cookie and is thought to derive its
name from the brown color of the cookie. Folklore has its origin coming
from a careless cook that forgot to put baking powder in the chocolate cake
batter recipe.

It wasn’t until the 1906 edition that chocolate was added to the original recipe, which still was made in individual pans.

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