Preheat your oven to 350°F (175°C) for even baking.
Grease and flour two 9-inch round cake pans to prevent sticking.
In a mixing bowl, whisk together the cake flour, baking powder, and salt. Set aside.
In another bowl, beat the unsalted butter, granulated sugar, and grapeseed oil with an electric mixer on medium speed until light and fluffy, about 3-5 minutes.
Add the large eggs and egg yolks one at a time, mixing well after each addition. Then mix in the vanilla and butter extracts.
Add the sour cream to the butter mixture and mix until fully combined for extra moistness.
Gradually add the dry ingredients to the wet mixture, mixing on low speed until just combined. Be careful not to overmix!
Divide the batter evenly between the prepared cake pans.
Bake in the preheated oven for 25-30 minutes or until a toothpick inserted in the center comes out clean.
Once baked, remove the cakes from the oven and let them cool in the pans for about 10 minutes. Then, transfer them to a wire rack to cool completely.