Mix dry ingredients in a stand mixer with a paddle attachment. Add liquid ingredients and mix until incorporated. Scrape bowl in between mixing.
Bake at 350 F, until toothpick comes out clean and has a bouncy spring when pressed in the middle of the cake.
For the Peanut Butter Buttercream:
Place sterilized stand-up mixing bowl (just make sure it's super clean and dry) with whites on top of a saucepan with water, barely simmering (a.k.a. double boiler).
Heat to 160 F, constantly stirring. Be sure to watch it and keep stirring or else it'll turn into an omelette.
Add Cream of Tartar and whip in stand mixer until cool. Place in refrigerator or freezer if necessary, after reaching a medium peak. You can also place the cooked egg whites on an ice bath ahead of time and place it in the refrigerator, then whip it up.
Place back on whip and gradually add butter, one stick at a time. Make sure the meringue is cold prior to adding it to the mixture or else it will be a soupy mess. The mixture should separate at first (don't be alarmed and freak out). Be patient and keep mixing; it'll come back together. Mix until smooth and well incorporated.
Add peanut butter and vanilla. Mix until smooth and well incorporated.
For the Ganache:
Place chocolate in a bowl.
Place heavy cream in a microwave safe bowl and heat in microwave until scalding hot. Avoid overboiling.
Stir lightly until mixture thickens. Set aside to room temperature, ready for spreading on cake.
For the Assembly:
Start with a base of chocolate cake. Make a barrier of buttercream with a piping bag. Fill and spread with a thin layer of peanut butter. Spread a thin layer of ganache on top.
Place another layer of cake and repeat the process.
Crumb coat, chill and final coat your cake. Serve and enjoy.