Step 1

Preheat oven to 350°F/175°C. Line four 7" or three 8" pans with parchment paper, then grease with nonstick spray or homemade cake release. Set aside.

Step 2

Mix 3 cups all purpose flour, 3 cups sugar, 2 1/2 tsp baking powder and 1 tsp salt together in a stand mixer with a paddle attachment or hand mixer until fully combined.

Step 3

Then, mix in 1 cup of room temperature, unsalted butter slowly into the dry ingredients on a low speed. Continue to mix until no large chunks of butter remain, and the mixture looks like moist sand.

Step 4

Pour in 1 cup of egg whites and mix on low until just incorporated. Scrape the sides and bottom of the bowl as needed with a rubber spatula.

Step 5

Then mix in 1 1/2 cups sour cream, 2 Tbsp of vegetable oil, and 1 Tbsp of vanilla bean paste on a low speed until fully incorporated.

Step 6

Scrape down the sides of the bowl with a rubber spatula one more time, then beat on a medium speed for about 30 seconds to make sure everything is properly mixed together. This also helps lighten the texture of the cake layers.

Step 7

Divide the batter evenly between the prepared pans. I like to use a scale to make sure each pan has the same amount of batter and will bake up to be the same height.

Step 8

Bake for 33-35 minutes or until a toothpick comes out with a few moist crumbs. Rotate the pans halfway through to help them bake evenly.

Step 9

Let the pans cool for 10 minutes, then run a small offset spatula around the perimeter of the pan to separate the cake from the pan.

Step 10

Place the cake layers into the freezer for 30 minutes to accelerate the cooling process. Once the layers are fully cooled, carefully flip the pans and remove the layers.

Step 11

Use a serrated knife to level the tops of the layers right before you plan to assemble your cake, or you can wrap and freeze them if you're making them in advance.

Step 12

If you do freeze the cake layers, let them thaw for about 20 minutes before making the cake. The cake layers should still be slightly cold to the touch, which will make it easier to assemble the cake.

Step 13

While the cake layers bake and cool, make the vanilla bean buttercream frosting.

Step 14

In the bowl of a stand mixer or a large bowl, beat 2 cups of unsalted butter on a medium speed for 30 seconds with a stand mixer and paddle attachment or hand mixer until smooth.

Step 15

Mix in 2 Tbsp of vanilla bean paste and 1/2 tsp salt on a low speed. Gradually mix in 7 cups of powdered sugar and 1/4 cup of heavy cream on a low speed.

Step 16

Continue to mix on a low speed for a few minutes until the desired consistency is reached.  If the frosting seems too thick, add in additional cream (1 Tbsp at a time). If the frosting seems too thin, add in more powdered sugar (quarter of a cup at a time).

Step 17

If you plan to color the buttercream, add in the gel food coloring once the frosting is fully made, and beat on low until it reaches the desired color.

Step 18

Cover the buttercream flush with plastic wrap to prevent crusting, then set aside.

Step 19

Stack and frost cake layers on a greaseproof cake baord or flat plate using a dab of frosting to help stick the first cake layer to the board.

Step 20

Spread an even layer of buttercream between each cake layer with a large offset spatula. Add a thin coat of frosting around the cake to fully cover the cake layers.

Step 21

Smooth using a bench scraper, then chill the cake in the fridge (30 minutes) or freezer (10 minutes) until the frosting is firm to the touch.

Step 22

Add a second, thicker layer of frosting to the cake and smooth using a bench scraper. Then decorate as desired and enjoy! I used a Wilton 1M piping tip to decorate the top of the cake, but any open star piping tip would work great!