Step 1: Preheat your oven to 350°F (175°C). Grease your cake pans and line the bottoms with parchment paper for easy removal later.
Step 2: In a medium bowl, whisk together the cake flour, baking powder, and salt. Set this mixture aside.
Step 3: In a large mixing bowl, beat the unsalted butter, granulated sugar, and grapeseed oil together until light and fluffy. This should take about 3-4 minutes.
Step 4: Add the eggs and egg yolks one at a time, mixing well after each addition. Stir in the vanilla and butter extracts until fully combined.
Step 5: Gradually add the dry ingredients to the wet mixture in three additions, alternating with the sour cream. Start and end with the flour mixture, mixing until just combined.
Step 6: Evenly distribute the batter between the prepared cake pans. Bake in the preheated oven for 25-30 minutes, or until a toothpick comes out clean from the center.
Step 7: Once baked, remove the cakes from the oven and let them cool in the pans for about 10 minutes. Then, transfer them to a cooling rack to cool completely.
Step 8: In a large bowl, beat the slightly cold unsalted butter until creamy. Gradually add the sifted confectioner's sugar, mixing until well combined. Add the vanilla extract and a pinch of salt. If the frosting is too thick, add the heavy whipping cream until reaching your desired consistency.
Step 9: Place one cake layer on a serving plate and spread a generous amount of frosting on top. Place the second layer on top and frost the top and sides of the cake. Decorate with chocolate chips if desired.
Step 10: Slice into the cake and serve. Enjoy the delightful flavors and textures that make this yellow cake a favorite!