To make the brownies, adjust an oven rack to the middle level of the oven and preheat to 350°F.

Prepare a 9 by 13-inch baking pan with heavy-duty aluminum foil. (shown on page xvi). Lightly grease the foil in the pan.

Cut the butter sticks into 1-inch slices. In a small, heavy saucepan, melt the butter pieces over the lowest setting; add the bitter-sweet chocolate chips. Stir with a small whisk until combined and the chocolate is melted and smooth. Turn off the heat but leave the saucepan on the burner while proceeding with the recipe.

Using a large whisk, lightly beat the eggs in a large mixing bowl. Place the sugar and salt in a separate small mixing bowl, then whisk into the eggs just until incorporated. Briefly whisk the melted chocolate mixture, then gradually whisk into the egg mixture until just combined. Briefly whisk in the vanilla.

Place the flour and cocoa powder in the small mixing bowl; whisk together to combine. Sift through a medium strainer directly onto the batter; stir in with a silicone spatula until just combined. Pour the batter into the prepared pan and spread evenly with a small offset spatula. Bake for 34 minutes, until a toothpick inserted in the center, comes out clean.

Transfer the pan to a cooling rack and let cool at room temperature for at least 15 minutes, then refrigerate the pan for 7 to 8 hours, or overnight. See page xix for instructions on removing and cutting the slab, and for refrigerated storage (up to 3 weeks) and freezing guidelines.