Preheat your oven to 350°F (175°C). Prepare two 9-inch round cake pans by greasing them with butter or non-stick spray. Dust with flour to prevent sticking.

In a large mixing bowl, beat the 7 egg yolks with 3/4 cup of sugar. Use an electric mixer until the mixture becomes pale and thick. This should take about 5 minutes.

Add the champagne, vegetable oil, and vanilla extract to the egg yolk mixture. Mix until well combined. Gradually sift in the cake flour, cocoa powder, baking powder, salt, espresso powder, and orange zest. Mix until just combined.

In a separate bowl, whip the 7 egg whites until soft peaks form. Gradually add the remaining 3/4 cup of sugar while continuing to whip. Beat until you achieve stiff peaks.

Gently fold the whipped egg whites into the chocolate mixture. Do this in three additions, being careful not to deflate the egg whites. The batter should be light and airy.

Pour the batter evenly into the prepared cake pans. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean. Let the cakes cool in the pans for a few minutes before transferring them to wire racks to cool completely.

If you want to frost the cake, consider using whipped cream or a light chocolate frosting. This is entirely optional since the cake is delicious on its own!