Source: The Farm of Beverly Hills - Beverly Hills, California

1 1/2 cups (3 sticks) unsalted butter, cut into pieces
12 ounces fine-quality bittersweet chocolate
    (not unsweetened), chopped
6 large eggs
1 1/4 cups cake flour (not self-rising)
1 cup plus 2 tablespoons unsweetened cocoa powder
    (not Dutch process)
3 cups granulated sugar
1/2 teaspoon salt

Preheat oven to 350 degrees F. Butter and flour a 13 x 9-inch metal baking pan, knocking out excess flour.

Melt butter with chocolate in a large metal bowl set over a saucepan of barely simmering water, stirring until smooth. Remove bowl from pan and whisk in eggs, 1 at a time.

Sift together flour and cocoa powder in a separate bowl and stir into batter with sugar and salt. Pour batter into pan and bake in middle of oven until top is firm and a tester inserted into center comes out with crumbs adhering, 40 to 45 minutes. Cool completely in pan on a rack, about 2 hours, before cutting into giant squares.

Brownies keep, layered between wax paper in an airtight container, for 5 days.