High-Altitude Fudge Cake

Let's Cook

1. Step 1.

   Melt, stirring constantly, in a double boiler or heatproof bowl over barely simmering water: 4 ounces (115g) unsweetened chocolate, chopped, or 1 cup semisweet chocolate chips

2. Step 2.

   Whisk together thoroughly in a medium bowl: 2 cups sifted (200g) cake flour; 2 teaspoons baking powder; ½ teaspoon salt

3. Step 3.

   Beat in a large bowl, or in a stand mixer with the whisk attachment, until foamy: 3 large egg whites; ¼ teaspoon cream of tartar

4. Step 4.

   Gradually add and beat on high speed until soft, slightly droopy peaks form: ¼ cup (50g) sugar

5. Step 5.

   Set aside. Beat in another large bowl (or transfer the egg whites to another bowl and reuse the stand mixer bowl with the paddle attachment) until light and fluffy: 1 stick (4 oz or 115g) unsalted butter, softened; 2 cups (400g) sugar (reduce to 1 ½ cups [300g] if using chocolate chips); 2 teaspoons vanilla

6. Step 6.

   Scrape down the bowl and beat a few seconds longer. Beat in, blending well: 3 large egg yolks

7. Step 7.

   Beat in the melted chocolate. Scrape down the bowl. On low speed, add the flour mixture in 3 parts, alternating with: 1 ½ cups (355g) milk

8. Step 8.

   in 2 parts, scraping down the bowl and beating well after each addition. Gently fold in the whites by hand in 3 additions until the batter no longer looks streaky. Divide the batter between the round pans, scrape into the baking pan, or, for cupcakes, fill cups almost three-quarters full. Bake until a cake tester inserted into the center comes out clean, 35 to 40 minutes for layers or a sheet pan, 15 to 20 minutes for cupcakes.

9. Step 9.

   Let cool in the pan(s) on a wire rack for 10 to 15 minutes. Then unmold and cool completely. (The sheet cake can be cooled in and served from the pan.)