Begin by milling your soft white wheat berries into fresh flour. To get 300 grams of sifted flour, you’ll need to mill around 360-400 grams of berries—about 20-40% extra to account for bran loss and seasonal moisture. Use the finest setting on your grain mill. Once milled, sift the flour through a #60 sieve to remove the bran and create a delicate, cake-like texture. Set the sifted bran aside for another use, then weigh the sifted flour to ensure you have exactly 300 grams. Add more flour as needed to reach the full amount.

Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, a bundt pan, or line cupcake tins if using. For cupcakes, place the tins on a baking sheet to catch any potential drips.

In a large bowl, whisk together the sifted flour, cocoa powder, baking powder, baking soda, espresso powder, and salt. If you plan to long-ferment the batter overnight, omit the baking powder, baking soda, and salt and stir those in just before baking the next day.

In the bowl of a stand mixer fitted with the paddle attachment, beat the softened butter on medium speed for 2 to 3 minutes until light and fluffy. Add the granulated sugar and continue beating until the mixture is pale and aerated.

Add in the sunflower oil, sour cream, sourdough discard or starter, and vanilla extract. Mix on medium speed until smooth and creamy. Be careful not to overmix—especially once the sourdough is added.

Pour in the room temperature milk and stir just until combined. Scrape down the sides of the bowl to ensure everything is incorporated.

Gradually add the dry ingredients to the wet mixture in three additions, mixing on low speed after each addition. Stop mixing as soon as the batter looks smooth and uniform.

For overnight fermenting: At this point, cover the batter tightly and refrigerate. The next day, mix in the reserved baking powder, baking soda, and salt. Then proceed with the next steps.
For same-day baking: Continue directly to the next step.

In a clean, dry bowl, whip the room temperature egg whites using a hand mixer until stiff peaks form. This step adds volume and tenderness to your cake.

Gently fold one-third of the whipped egg whites into the batter using a rubber spatula. Once combined, fold in the rest of the egg whites until the batter is light and airy.

Evenly divide the batter between the two prepared cake pans. Use a kitchen scale if desired for accuracy. Smooth the tops of the batter and place in the oven. Bake for 25 to 30 minutes, or until a toothpick or cake tester inserted into the center comes out clean.

Let the cakes cool in the pans for about 10 minutes. Then turn them out onto a cooling rack and allow to cool completely before frosting.

Once the cakes are fully cooled, place one layer on a cake stand or serving plate. Spread a layer of frosting evenly over the top, then gently place the second layer over it. Apply a thin crumb coat to the whole cake and chill for 10 minutes in the freezer or 30 minutes in the refrigerator.

After chilling, frost the top and sides with the remaining buttercream. If your frosting has been refrigerated, let it sit at room temperature for 5 to 10 minutes to soften before using.

Slice and serve!