The plain version makes a trim but powerful bar. You can also stir 1 cup coarsely chopped walnuts, pecans, or macadamia nuts into the batter after the flour mixture.
Butter (for the pan)
1 cup sifted cake flour
2 tablespoons unsweetened alkalized cocoa powder (such as Droste)
1/8 teaspoon baking powder
1/8 teaspoon salt (preferably fine sea salt)
4 ounces unsweetened chocolate, melted and cooled to tepid
14 tablespoons (1 3/4 sticks) unsalted butter, melted and cooled to tepid
4 eggs 2 cups superfine sugar
2 teaspoons vanilla extract
Confectioners' sugar (for sprinkling)
1. Set the oven to 325 degrees. Lightly butter a 9-by-9-by 2-inch baking pan.
2. Sift the flour, cocoa powder, baking powder, and salt onto a sheet of waxed paper.
3. In a mixing bowl, whisk the chocolate and butter until smooth.
4. In another larger bowl, using a wooden spoon or flat wooden paddle, beat the eggs just to mix. Add the sugar and beat for 30 seconds just to blend it in without creating volume. Stir in the chocolate-butter mixture and vanilla.
5. Resift the flour mixture into the chocolate mixture. Whisk slowly to form a batter, scraping down the sides of the mixing bowl to keep the batter even-textured. Scrape the batter into the pan, smoothing it into the corners.
6. Bake the mixture for 30 minutes or until just set. It will be a thin-ish layer; the block will puff slightly and there will be a few hairline cracks around the edge.
7. Cool the pan on a rack. Refrigerate for 1 hour or until firm enough to cut.
8. With a knife, cut the square into quarters, then cut each quarter into 4 bars. Use a small offset spatula to remove the bars from the pan. Store in an airtight tin. If the kitchen is warm, refrigerate the tin. Just before serving, sift confectioners' sugar on top. Lisa Yockelson