Step 1

Preheat oven to 350 degrees (F). Grease two 9-inch round cake pans and set them aside.

Step 2

In a large mixing bowl, combine the cake flour, baking powder, baking soda, and salt. Set aside.

Step 3

In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using a handheld electric mixer, beat the butter on medium-high speed until creamy, about 1 minute. Add in the sugar and beat until light and fluffy, about 3 minutes. Beat in the eggs and egg yolks, one at a time, beating well after each addition and scraping down the sides of the bowl as needed. Beat in the vanilla. Turn mixer off for a moment.

Step 4

In a glass measuring cup, combine the milk and lemon juice.

Step 5

With the mixer speed on low, add the flour mixture in three additions, alternating with the milk mixture in two additions, and mixing just until the flour is incorporated. Do not over mix here.

Step 6

Divide the batter evenly among the prepared pans and smooth the tops with a rubber spatula.

Step 7

Bake for 25 minutes, or until the tops are golden brown and a toothpick inserted in the center of a cake comes out clean, or with moist crumbs attached.

Step 8

Cool the cakes in the pans on wire racks for 15 minutes.

Step 9

Invert the cake layers onto wire racks and cool completely.

Step 10

In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using a handheld electric mixer, beat the butter on medium-speed until completely smooth. Reduce the speed to low and gradually add in the confectioners' sugar, beating until all of the sugar is completely combined. Add in the chocolate and beat smooth. Once all of the ingredients have been incorporated, increase the speed to medium-high and beat for a minute.

Step 11

Frost cake as desired.