1. Preheat oven to 325° F/ 162° C.
2. Prepare two 8" OR two 9" cake pans, lining them with parchment paper first, then greasing them with butter and flour. Please note: I used 8" cake pans for this cake, and I baked a higher altitude thus my cakes required a slightly longer baking time. 
3. Sift together all dry ingredients in a big bowl.
4. In a separate small bowl, combine buttermilk and vanilla and set aside.
5. In an electric mixer with the paddle attachment, beat softened butter and sugar until light and fluffy, about 4-8 minutes.
6. Add one egg at a time to the butter + sugar mixture, scraping down the sides of the bowl with a spatula after each egg is incorporated. Beat for 15 seconds.
7. Add your yolks one at a time. Batter should be smooth.
8. Remove the bowl from the electric mixer and fold in the the dry ingredients with a spatula in 4 additions, alternating with the vanilla buttermilk mixture in 3 additions, beginning and ending with the dry ingredients.
9. Spoon batter into prepared cake pans and bake for 35mins to slightly over 1 hour. I know, the range of time is ridiculous. See my bakers note above, but don't be discouraged. The cake should be golden brown, and a cake tester should come out clean with a few crumbs stuck to it when inserted into the cake. Wait for the cake to cool completely before cutting into layers.

to assemble:

1. Cut each layer in half with a long serrated knife, creating 4 layers total and sandwiched each layer with a generous helping of lemon curd. I pipped my lemon curd layers in but you can easily spoon it on. Perfection is not our end game here, only deliciousness, so don't stress if the filling isn't perfectly even. I sure didn't.
2. Put a "crumb coat" of buttercream frosting on the cake, let that chill in the fridge to set for 20 minutes and then frost with the rest of the butter cream frosting.
3. Crumb coat = thin layer of frosting that brings all the crumbs to the party so you can frost it again without bringing the crumbs to the party.

1. Scrape the seeds from the vanilla bean pods and set aside. tip! Stick the scraped pods in your sugar container to make vanilla sugar! 
2. Fill a medium sized saucepan with a little bit of water (about 2-3 inches). The saucepan needs to be big enough to place a glass bowl on top, but make sure the bowl does NOT touch the water.
3. Put egg whites and sugar in the glass bowl that will fit over your medium sized saucepan.
4. Bring the water in the medium sized saucepan to a gentle simmer. Place the glass bowl on top of the saucepan and whisk gently for about 8-10 minutes, or until mixture becomes 160°F / 71°C. You'll know it's ready because the mixture should be too hot to hold your finger in the mixture for a long time, but not too hot to touch.
5. Remove egg white mixture from the heat and pour into your electric mixing bowl. With the whisk attachment whisk heated egg whites and sugar until it looks like a stiff cloud or shaving cream. The mixture should cool as it whips, and the outside of the bowl should feel room temperature.
6. On a medium speed, add the butter 1 tablespoon at a time, until the butter is fully incorporated, scraping the bowl about halfway.
7. Add vanilla bean seeds, extract and salt and whip for 30 seconds.
8. Use buttercream immediately, or store in the fridge in an air-tight container for up to 3-5 days. Take care that buttercream can absorb any flavor it's around, so it's important that it's sealed well. See *bakers note above if you'd like to store it chilled for a few days.