The first book was by Fannie Farmer, the second by a Boston-area chocolate purveyor, Walter Lowney (then a major competitor of Baker’s). All three recipes called for unsweetened chocolate, as did most versions up though the 1950s. (Check out Lowney's brownies here--a fine classic recipe.)
Now maybe you don’t really care about this, but because I’m a serious culinary history buff I’m compelled to point out that some sources wrongly say that brownies initially appeared in the 1890s. I’ve gone and investigated, and although several earlier goodies were named brownies, they were not the brownies we’re talking about here. One so-called “brownie” was a candy, another was a cookie made brown with molasses. (Try serving the molasses ‘brownie” today, and see what happens!)
Bake, middle rack, until a toothpick inserted in the center comes out clean, about 24 to 28 minutes; if the pick comes out with wet batter clinging to it, continue several minutes longer, then check again. Continue, checking until just barely baked through. Immediately sprinkle some fine peppermint shards over top, if desired, then set the pan on a rack to cool completely.
Shauna Ahern's Gluten-Free Peanut Butter Brownies , left.