I resist the term fudgy — it is inadequate for these exceptional brownies. They are densely creamy and intensely bittersweet beneath a paper-thin nuance of crust on top.
The late Robert Steinberg (cofounder of Scharffen Berger Chocolate) created the recipe for the company’s first chocolate, Scharffen Berger Bittersweet 70% Chocolate. I published the recipe in Alice Medrich’s Cookies and Brownies in 1997, and it appeared again in The Essence of Chocolate by John Scharffenberger and Robert Steinberg in 2006. It remains a go-to modern recipe for very chocolaty brownies that are not excessively sweet.
Preheat the oven to 350 degrees. Position a rack in the lower third of the oven.
Melt the butter with the chocolate in a medium heatproof bowl set directly in a wide skillet of barely simmering water. Stir frequently until the mixture is melted and smooth and fairly hot to the touch. Remove the bowl from the water. Stir in the sugar, salt, and vanilla, if using. Add 1 egg, stirring until it is incorporated. Repeat with the second egg. Stir in the flour and beat with a wooden spoon or spatula until the batter is smooth and glossy and comes away from the sides of the pan; it is critical that the batter pull itself together, so don’t stop mixing until it does. Stir in the nuts, if using. Scrape the batter into a foil-lined 8-by-8-inch pan.
Spread the batter evenly but with lots of raised swirls and ridges — these look great and get slightly crusty in the oven. Bake for 30-35 minutes, until a toothpick inserted in the center comes out with a few moist crumbs, not totally gooey.
Cool on a rack. Lift the foil ends to transfer the brownies to a cutting board. Cut into 16 squares.