Step 1

Preheat the oven to 350°F (175°C).

Step 2

Spray two 8" round cake pans or one 9x13 cake pan with nonstick baking spray.

Step 3

In a mixing bowl, cream together the butter and sugar on high speed for 3 minutes.

Step 4

Mix in the eggs one at a time, followed by the egg yolks and vanilla extract.

Step 5

Mix in the buttermilk until well combined.

Step 6

In a separate bowl, combine the flour, salt, and baking powder.

Step 7

Gradually add the dry ingredients to the wet ingredients, mixing until smooth.

Step 8

Pour the batter into the prepared cake pan(s).

Step 9

Bake for 25-33 minutes until the tops are light golden brown, there is no jiggle, and a toothpick inserted into the center comes out clean.

Step 10

Allow the cake to cool completely in the pan.

Step 11

In a mixing bowl, combine the butter, 4 cups of powdered sugar, cocoa powder, vanilla extract, and 3 tbsp of heavy cream.

Step 12

Mix until smooth. If using dairy-free butter, adjust the consistency as needed by adding more heavy cream.

Step 13

If the frosting is too soft, add more powdered sugar, 1/2 cup at a time, until firm enough to spread onto the cake.

Step 14

Once the cake is completely cooled, spread the chocolate buttercream frosting evenly over the top.

Step 15

If desired, decorate with additional toppings such as sprinkles or chocolate shavings.

Step 16

Slice and serve the cake and enjoy the delightful combination of moist yellow cake and rich chocolate buttercream frosting.