Preheat the oven to 350 degrees F (180 degrees C). Grease and line two 6 inch cake pans with parchment paper.

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

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

Add the oil, yogurt, milk, egg, and vanilla, and mix until fully combined.

Divide the batter evenly between the prepared cake pans. (I recommend weighing the batter to be as precise as possible!)

Bake for 28-32 minutes or until a tooth pick inserted comes out clean.

Cool completely before frosting.

In a double boiler, heat the egg whites, sugar, and salt, whisking frequently until it reaches 160 degrees F (70 degrees C) 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 (30 degrees C).

Cut the butter into cubes and add to the meringue a few pieces at a time, allowing them to fully incorporate before adding more. 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.

Add the vanilla and mix until fully incorporated.

Secure the first layer of cake 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.

Cover the whole cake in a thin layer of frosting for the crumb coat.

Place in the fridge for about 20 minutes, then frost the cake as desired.

Top with rainbow jimmy sprinkles and enjoy!