FOR THE CAKE:
1 cup (226 g) unsalted butter, room temperature
1/3 cup (72.6 g) canola oil
1 teaspoon (5.6 g) salt
1 3/4 cups (350 g) granulated sugar
5 whole eggs, room temperature
2 eggs yolks, room temperature
3 cups (345 g) cake flour
2 teaspoons (8 g) baking powder
1 cup (240 g) sour cream, room temperature
1 teaspoon (4.2 g) clear vanilla extract
1 teaspoon (4.2 g) butter extract
FOR THE CHOCOLATE FROSTING:
2 cups (452 g) unsalted butter, slightly cold
5 cups (625 g) powdered sugar, measured and then sifted
1 tablespoon(13 g) pure vanilla extract
Pinch of salt
8 oz. (150 g) good quality semi-sweet or dark chocolate, chopped, melted and cooled
1/4 cup (57.75 g) heavy whipping cream
FOR THE CAKE:
Preheat the oven to 350 degrees F. Spray three 8-inch or four 6-inch round cake pans with non-stick spray, add parchment and another coat of spray. Set aside.
In a medium size bowl, sift the cake flour and baking powder. Set aside.
In the bowl of a stand mixer, fitted with the paddle attachment, beat the butter, canola oil, salt and sugar on high until fluffy and smooth, about 5 minutes.
Add the eggs and egg yolks, one at a time to the bowl and beat on medium until well incorporated.
Turn the mixer on low and add 1/3 of the flour mixture to the butter mixture and mix until fully incorporated. Then add half of the sour cream and blend well, followed by another 1/3 of the flour mixture, the second half of the sour cream and lastly, add the remaining flour mixture and mix until incorporated.
Add the clear vanilla extract and butter extract and beat on low until incorporated. Scrape down the sides of the bowl and mix on low for another 30 seconds.
Evenly distribute the cake batter among the three pans and bake for 25-30 minutes or until a toothpick inserted into the middle of the cakes comes out clean or with just a few crumbs. Make sure not to over bake.
Remove cakes from the oven and let cool in pans for 10 minutes before inverting onto cooling racks.
Once completely cooled, wrap in plastic wrap and place in the freezer or refrigerator to chill before frosting.
FOR THE FROSTING:
In a bowl fitted with a paddle attachment, combine beat the butter on medium-high until light and fluffy.
Turn the mixer to medium-low and gradually add the melted chocolate. Stop the mixer and scrape down the sides of the bowl. Beat again for about one minute.
With the mixer on low speed, gradually add the powdered sugar, vanilla extract, salt, and heavy whipping cream.
Increase the speed to medium-high and beat for another 2-3 minutes, until light and fluffy.
Stir by hand to push out air pockets.
After leveling each cake layer, place the first cake layer (top side/crumbly side up) on a cake board that has a little frosting on it (which acts like glue to hold the cake in place).
Spread about 1 cup of the frosting over the cake layer. Place the second cake layer on top and add another cup of frosting. Make sure to get eye level with the cake to check that your frosting is spread evenly across each cake layer.
When you get the final cake layer, place it top side down on the second layer of frosting. Spread a thin coat of frosting around the entire cake to lock in the crumbs. Freeze the cake for 10 minutes to set the crumb coat.
Continue to frost and decorate the cake with the remaining frosting.