Stepwise Method

• Preheat your oven to 350°F (175°C). Grease your round cake pans and line them with parchment paper to ensure easy removal later. Set aside.
• In a medium bowl, sift together the all-purpose flour, baking powder, baking soda, and salt. Whisk to combine and set aside.
• Using your stand mixer or hand mixer, beat the ½ cup of unsalted butter and granulated sugar on medium speed until light and fluffy, about 3-5 minutes.
• Add the eggs one at a time, mixing well after each addition. Stir in the teaspoon of vanilla extract.
• Reduce mixer speed to low. Add the dry ingredients in three parts, alternating with the buttermilk in two parts, beginning and ending with dry ingredients. Mix until just combined after each addition. Avoid overmixing.
• Divide the batter evenly between the prepared pans. Smooth the tops with a spatula. Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean. Cool in pans for 10 minutes, then transfer to wire racks to cool completely.
• In a large bowl, beat the 20 tablespoons of unsalted butter until creamy. Sift together the powdered sugar and Dutch-processed cocoa powder, then gradually add to the butter, mixing on low speed. Add a pinch of salt, the light corn syrup, and vanilla extract. Slowly mix in the melted and slightly cooled chocolate until smooth and luscious.
• Place one cake layer on your serving plate. Spread a generous layer of chocolate frosting on top. Place the second cake layer on top and frost the entire cake with the remaining frosting. Use a large icing spatula to create smooth or textured designs.
• Refrigerate the cake for at least 30 minutes to set the frosting. Bring to room temperature before slicing and serving.