Peanut butter lovers, this cake is for you! Peanut butter cake layers studded with peanut butter chips covered in a peanut butter Swiss meringue buttercream.
Preheat oven to 350F. Grease and flour three 6" cake rounds and line with parchment.
In a medium bowl, whisk flour, baking powder, and salt until well combined. Set aside. In a measuring cup, whisk milk and powdered peanut butter, set aside.
Using a stand mixer fitted with a paddle attachment, cream butter, oil, and peanut butter until smooth. Add sugars and beat on med-high until pale and fluffy (3mins).
Reduce speed and add eggs one at a time fully incorporating after each addition. Add vanilla.
Alternate adding flour mixture and peanut butter milk, beginning and ending with flour (3 additions of flour and 2 of milk). Fully incorporating after each addition.
Fold in peanut butter chips (that have been tossed in 1 Tbsp flour) and mix until just incorporated. Do not overmix.
Bake for 40-45 mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10mins then turn out onto wire rack. Allow cakes to cool completely.
Peanut Butter Swiss Meringue Buttercream:
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.*
Place bowl over a pot with 1-2" of simmering water and stir constantly with a whisk until the mixture is hot and no longer grainy to the touch or reads 160F on a candy thermometer (3mins)
Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth.
Add powdered peanut butter 1 Tbsp at a time & vanilla. Whip until smooth.**
Assembly:
Place one layer of cake onto a cake stand or serving plate. Top with approximately 3/4 cup of buttercream, sprinkle with 1/4 cup chopped peanuts. Repeat with remaining layers and crumb coat the cake. Chill for 20mins.
Frost the top and sides of the cake with remaining buttercream. I started by spreading a generous amount of buttercream on the top and letting it overhang on the sides. Then I used a flat spatula to add buttercream to the sides of the cake and to smooth the which created a top lip with the overlapping buttercream.
Add a small dollop of buttercream into the top center and spread roughly. Sprinkle chopped peanuts on the top and along the bottom if desired.
Notes
* Ensure there is NO trace of egg yolks in your whites and that your mixer bowl and whisk is completely grease free or your meringue won't stiffen. ** The buttercream may look like it's curdled at some point. Keep mixing until it is completely smooth.