Brownies are so very rarely made from scratch. As with mayonnaise or marshmallows, the idea of starting from the beginning is simply obsolete. Homemade brownies, the kind you make without the box, may well be on their way to extinction.
I have two theories. One is that people are of the delusional thinking that brownies are difficult to make, which they are not. Basically you melt some butter and chocolate, add eggs, maybe vanilla, a heap of flour, stir, pour and bake. It's right up there with boiling pasta. Making cookies is slightly harder.
The second theory is that people believe that brownies baked from scratch will be no better than those made from a mix. We settle for "pretty good," as my friend described his from-the-boxers, because it seems impossible to make a brownie that tastes as good as those costing in the neighborhood of $2 in a decent bakery. But, as someone who spent a summer baking sheetpan after sheetpan of serious chocolate brownies in one such bakery, I am here to tell you that there is no secret. But there is one consideration that outranks the rest. Baking time. Those brownies you see stacked so high and chocolate-mighty in bakeries are gooey and rich not because the chocolate in them is worth its weight in gold (though the better the chocolate, the better the brownie). And not because they were baked in a special oven, or by someone with lofty training. Those brownies were simply baked for just the right amount of time. Maybe less.
In the beginning, as you get to know your oven and gain your brownie-baking confidence, check them a lot. Shake the pan. If batter moves around, they need to cook more. If you stick a toothpick in and it comes out clean, you've gone too far. Overcooking brownies--or, rather, not undercooking brownies--will result in a dry, cakey square no better than the chocolate-flavored things from the box.
Just to prove a point (that's how I am), I made a few batches of brownies for the aforementioned friend. And, as if I meant to (which I did not), I accidentally fully-cooked one tray. "It's cake," the baking friend said, putting down that brownie and reaching for one from the cooked-just-enough batch. He bit into it. He smiled. He shook his head in disbelief and, with his mouth still full, confessed, "It's perfect."
6 ounces unsweetened chocolate, broken into large chunks
6 ounces unsalted butter
3 cups sugar
1 tablespoon vanilla
1 tablespoon instant espresso
1 teaspoon salt
3 cups flour
1 cup walnuts, coarsely chopped (optional)
Place chocolate chunks and whole sticks of butter in a metal roasting pan and place in a 200-degree oven until melted. Remove pan from oven, set on a counter and stir with a wooden spoon to combine. Allow to cool to room temperature. Beat eggs and sugar together until light and fluffy. Add cooled chocolate mixture and stir to combine. Stir in vanilla, espresso, salt, and flour until no flour is visible. Add walnuts if using. Pour into buttered sheetpan and bake in 350-degree oven for 25-30 minutes. Brownies are done when a toothpick inserted into the center comes out with traces of melted chocolate and moist crumbs and when the center no longer shakes when you move pan back and forth.