Fluffy Yellow Layer Cake with Chocolate Frosting

1. Prepare the oven and baking pans

Start by preheating your oven to 350°F and preparing your baking pans. Adjust the oven rack to the middle position, then grease two 9-inch round cake pans. Line the bottoms with parchment paper, grease the parchment, and lightly flour the pans to ensure your cakes release easily after baking.

2. Combine dry ingredients

In a large bowl, whisk together the cake flour, baking powder, baking soda, salt, and 1.5 cups of the granulated sugar. This ensures that the leavening agents and salt are evenly distributed throughout the flour, which is key for an even rise.

3. Mix wet ingredients

In a separate medium bowl, whisk together the melted and cooled butter, buttermilk, vegetable oil, vanilla extract, and egg yolks until smooth and well combined.

4. Whip egg whites

Using a stand mixer fitted with the whisk attachment, whip the egg whites and a pinch of cream of tartar on medium speed until they become foamy. Gradually add the remaining 0.25 cup of sugar, increasing the speed to high, and whip until stiff peaks form. This step is crucial as whipping air into the egg whites will give your cake a light and fluffy texture. You'll know they're ready when the peaks are glossy and stand tall without drooping.

5. Combine dry and wet ingredients

Add the dry ingredients to the stand mixer bowl. Pour in the wet mixture and mix on low speed until just incorporated, then scrape down the sides of the bowl. Increase the speed to medium and beat until the batter is smooth, about 10 to 15 seconds. Be careful not to overmix.

6. Fold in egg whites

Gently stir one-third of the whipped egg whites into the batter to lighten it. Then, using a rubber spatula, carefully fold in the remaining egg whites until no streaks remain. This folding technique helps maintain the airiness of the batter.

7. Bake the cakes

Divide the batter evenly between the prepared pans, smoothing the tops with a spatula. Give the pans a gentle tap on the counter to release any large air bubbles. Bake for 20 to 22 minutes, or until a toothpick inserted into the center comes out clean. Allow the cakes to cool in their pans for 10 minutes before transferring them to a wire rack to cool completely, about 2 hours.

8. Prepare the frosting

While the cakes are cooling, prepare the frosting. In a food processor, combine the softened butter, confectioners' sugar, cocoa powder, and a pinch of salt. Process until the mixture is smooth and creamy. Add the corn syrup and vanilla extract, followed by the melted and cooled chocolate. Process until the frosting is velvety and fully combined.

9. Assemble the cake

Once the cakes are completely cool, it's time to assemble. Place one cake layer on a serving plate and spread a generous amount of frosting on top. Place the second layer on top, then cover the entire cake with the remaining frosting, smoothing it out with a spatula for a beautiful finish.