For other uses of "Brownie", see Brownie
A chocolate brownie is a flat, baked square or bar developed in the United States at the end of the 19th century and popularized in both the U.S. and Canada during the first half of the 20th century. The brownie is a cross between a cake and a cookie in texture. Brownies come in a variety of forms. They are either fudgy or cakey, depending on their density, and they may include nuts, frosting, whipped cream, chocolate chips, or other ingredients. A variation that is made with brown sugar and no chocolate is called a blondie.
Brownies are common lunchbox fare, typically eaten by hand, and often accompanied by milk or coffee. They are sometimes served warm with ice cream (à la mode), topped with whipped cream or marzipan, or sprinkled with powdered sugar. They are especially popular in restaurants, where they can be found in variation on many dessert menus.
A chef at Chicago's Palmer House Hotel created the confection after Bertha Palmer requested a dessert for ladies attending the fair; it should be, she said, smaller than a piece of cake, though still retaining cake-like characteristics and easily eaten from boxed lunches. These first brownies featured an apricot glaze and walnuts, and they are still being made at the hotel according to the original recipe.
The earliest published recipes for a brownie like those of today appeared in the Home Cookery (1904, Laconia, NH), Service Club Cook Book (1904, Chicago, IL), The Boston Globe (April 2, 1905 p. 34) and the 1906 edition of The Boston Cooking School Cook Book by Fannie Merritt Farmer. These recipes produced a relatively mild and cake-like brownie. The name "brownie" first appeared in the 1896 version of the cookbook, but this was in reference to molasses cakes baked individually in tin molds, not true brownies.
A second recipe appeared in 1907 in Lowney’s Cook Book, by Maria Willet Howard and published by the Walter M. Lowney Company of Boston, Massachusetts. This recipe added an extra egg and an additional square of chocolate to the Boston Cooking School recipe, creating a richer, fudgier brownie. The recipe was named Bangor Brownies, possibly because it was created by a woman in Bangor, Maine. The Bangor Brownie went on to be rated third in the top 10 snacks a few years later.
Brownies with chocolate chunks
Myths about creation 
There are three main myths about the creation of the brownie. The first, that a chef accidentally added melted chocolate to biscuit dough. The second, a cook forgot to add flour to the batter. And thirdly, the most popular belief, that a housewife did not have baking powder and improvised with this new treat. It was said that she was baking for guests and decided to serve these flattened cakes to them. This became our beloved treat of today. Whatever may be the case; all three myths have gained popularity throughout the years due to its mysterious beginnings.
See also