• Preheat your oven to 350F (175C) and prepare two 8-inch round cake pans (they must be at least 2” deep) by lining each of the bottoms with a round of parchment paper and generously spraying the sides with baking spray.
• In a stand mixer (or you may use a large bowl and an electric mixer) stir together flour, sugar, baking powder, and salt until thoroughly combined.
  2 ¾ cup cake flour¹, 2 cups granulated sugar, 1 Tablespoon baking powder, 1 teaspoon salt
• Turn your mixer to low speed and add butter, one tablespoon at a time, not adding the next tablespoon until the first is incorporated. When you’re finished, the mixture should resemble coarse sandy crumbs (see photo in post or video above for visual).
  6 Tablespoons unsalted butter
• Add oil and stir until combined.
  ⅔ cup avocado oil, canola oil or vegetable oil
• In a measuring cup, whisk together milk, sour cream, and vanilla extract and stir into batter until thoroughly incorporated.
  ¾ cup whole milk, ½ cup sour cream, 1 Tablespoon clear vanilla extract²
• In a separate clean, dry, and grease-free bowl use clean beaters to beat egg whites to stiff peaks (I show a visual of this in the post above and in the video).
  6 large or extra large egg whites
• Use a spatula to gently fold egg whites into batter (don’t overmix, but make sure there are no lumps of egg white remaining).
• Portion 3 cups (580 grams) of batter into a separate bowl (you’ll be left with 5 cups in your first bowl), we’ll be making this into chocolate batter.

To make chocolate batter

• In a large measuring cup, stir together hot water and cocoa powder (it will be thick!). Add sour cream and sugar and whisk until well combined, then stir into your smaller bowl of batter and use a spatula to carefully stir together until completely combined.
  ¼ cup dark cocoa powder³, 2 Tablespoons very hot or boiling water, 2 Tablespoons sour cream, 2 Tablespoons granulated sugar
• Dollop approximately ⅓ cup of white batter into the center of each of your prepared cake pans. Using a clean scoop, scoop just shy of ⅓ cup of chocolate batter and drop that directly onto the center of the white batter. Repeat, alternating batter flavors, until you have used all of the batter. Take a reasonable amount of care so that your white batter doesn’t touch another ring of white batter nor does a ring of chocolate overlap with any of the other chocolate batter, this will keep your stripes looking like stripes and not like marbled swirls (more about this in the post).
• Carefully transfer pans to 350F (175C) oven and bake for 35-40 minutes or until a toothpick inserted in the center comes out clean or with moist crumbs. Allow to cool in pans for 15 minutes then run a knife around the edges of the cake to loosen from the sides (if needed) and carefully invert onto a cooling rack to cool completely.
• If needed, carefully level the cakes with a sharp serrated knife once completely cooled.
• Decorate using my white chocolate icing linked to in the ingredients, or with your frosting of choice (see notes for some of my favorite recommendations for this cake).
  1 batch White Chocolate Frosting