Preheat the oven to 350 degrees. Grease and line a 6 inch cake pan with parchment paper. 

In the bowl of a stand mixer fitted with the paddle attachment, sift the flour, sugar, baking powder, and salt, then whisk to combine. 

In a separate bowl combine the oil, yogurt, milk, and vanilla.

Cut up the butter into small cubes and add to the dry ingredients. Mix on low speed until it resembles wet sand. 

Add half of the wet ingredients to the dry, then scrape down the bowl. Add the rest of the wet ingredients and mix until just combined. 

In a separate bowl, whip the egg white to soft peaks. Gently fold it into the batter.

Pour batter into the prepared pan and bake for 25-28 minutes.

Grease and line a 6 inch cake pan with parchment paper. 

In the bowl of a stand mixer fitted with the paddle attachment, sift the flour, sugar, baking powder, and salt, then whisk to combine. 

In a separate bowl combine the oil, yogurt, milk, vanilla, and pureed strawberries.

Cut up the butter into small cubes and add to the dry ingredients. Mix on low speed until it resembles wet sand. 

Add half of the wet ingredients to the dry, then scrape down the bowl. Add the rest of the wet ingredients and mix until just combined. 

In a separate bowl, whip the egg white to soft peaks. Gently fold it into the batter.

Pour batter into the prepared pan and bake for 28-30 minutes.

Grease and line a 6 inch cake pan with parchment paper. 

In a medium sized bowl, sift the flour, cocoa powder, baking powder, and salt, then whisk to combine. 

In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar together for 1-2 minutes. Add the oil and egg and beat on high for 2 minutes. 

In a separate bowl, combine the yogurt, milk, and vanilla.

Alternate adding the dry ingredients and the yogurt-milk mixture to the fat-sugar-egg mixture. Do not over mix. Scrape down the bowl with a rubber spatula, then transfer to the prepared pan. 

Bake the chocolate cake for 32-35 minutes. 

In a double boiler, heat the egg whites, sugar, and salt, whisking frequently until it reaches 160 degrees F or until the sugar is completely dissolved and the egg whites do not feel grainy.

Transfer the egg white mixture into a bowl of a stand mixer with a whisk attachment. Whisk on high speed until stiff peaks form. Turn the mixer down to low speed, and wait until the meringue cools down to at least 85 degrees F.

Cut the butter into cubes and add to the meringue one piece at a time, allowing each piece to fully incorporate before adding the next. Once all of the butter is added, it will likely look curdled, but keep beating for a few more minutes and it will come together.

Once the buttercream has mostly come together, change the whisk attachment to the paddle and keep mixing on low speed until homogenous and smooth. 

Divide the buttercream equally into three bowls. In the first bowl, stir in vanilla, in the second strawberry jam, and in the third melted chocolate. You can add pink food gel to the strawberry buttercream if you would like. 

Secure the chocolate cake layer on the cake stand with a small amount of frosting on the bottom. Use a cookie or ice cream scoop to measure out the frosting for each layer. I used a 3 tablespoon cookie scoop and put 3 scoops of frosting on each layer. Add the chocolate buttercream to this layer, then place the strawberry cake layer on top. Add 3, 3tbsp of strawberry buttercream on top, then place the vanilla cake layer on top. 

If your cake layers were frozen overnight (which I highly recommend doing), then there is no need for a crumb coat. For this layered buttercream look, you'll start with the vanilla buttercream on the top and around the sides of the vanilla cake, making it as even and smooth as possible. Take this buttercream as far down as the top of the strawberry cake. 

Next, add the strawberry buttercream, layering over only about an inch of the vanilla buttercream. Do the same thing with the chocolate buttercream. 

Keep the cake at room temperature until ready to serve.