Using natural cocoa, which is slightly more acidic, gives the best results. Fill this cake with your favorite preserves, sweetened whipped cream, or any buttercream icing. For Christmas, this can be made into a Bûche de Noël. Please read About High-Altitude Cake Baking and About Roll Cakes. This recipe is designed for baking at 5,000 feet.

If baking at 7,000 feet, add ½ teaspoon cream of tartar. Bake for 9 to 10 minutes.

If baking at 10,000 feet, reduce the oven temperature to 350°F. Add 1 tablespoon flour, reduce the baking powder by ⅛ teaspoon, and increase the cream of tartar to 1 teaspoon. Bake for 9 to 10 minutes.

Have all ingredients at room temperature, about 70°F. Preheat the oven to 375°F. Grease a 15 ½ × 10 ½-inch jelly-roll pan, line the bottom with parchment paper, generously grease the paper, and dust with flour. This recipe will also work with a 17 ½ × 11 ½ × 1-inch pan, but the cake will be slightly thinner (check the cake for doneness early).

Whisk together thoroughly in a medium bowl:

Beat in a large bowl, or in a stand mixer with the whisk attachment, until foamy:

Gradually add and beat on high speed until soft, slightly droopy peaks form:

Set aside. Beat in another large bowl (or transfer the egg whites to another bowl and reuse the stand mixer bowl with the whisk attachment) on high speed until the batter is thick and a pale lemony color and forms a continuous flat ribbon falling back on itself when dropped from the beaters:

Fold in about one-third of the egg whites. Sprinkle about one-quarter of the cocoa-flour mixture onto the batter and fold in with a light touch to avoid losing volume. Repeat, alternately folding in the whites and cocoa-flour mixture; don’t worry if there are still a few streaks of white. Scrape the batter into the pan and spread it evenly. Bake until the top is springy to the touch and a toothpick inserted into the center comes out clean, 5 to 7 minutes; don’t overbake, or the cake will be dry.

Meanwhile, sift onto a clean kitchen towel in an area the size of the baking pan:

As soon as the cake is baked, invert the pan over the cocoa, lift off the pan, and peel off the paper liner. With a serrated knife, trim off about ⅛ inch of the crusty cake edges. Leave the cake flat until it cools completely, then spread with the desired filling, roll, see Cake Sheet for Roll Cakes, wrap, and refrigerate for at least 1 hour, or until firm. If not filling immediately, wrap tightly in plastic wrap to prevent it from drying out.