Instructions

For the Peanut Butter Cake

1. Preheat oven to 35o degrees F. Grease and flour three 6-inch pans. 
2. Sift together the flour, baking powder, salt, and cinnamon. Set aside.
3. In the bowl of an electric mixer fitted with a paddle attachment, mix together the butter and peanut butter until creamy. Add in the sugar and mix on medium for about 3 minutes. 
4. Decrease the speed to low and add in the vanilla and eggs, one at a time. Stop the mixer and scrape down the sides and bottom of the bowl.
5. With the mixer on low, add in half of the flour mixture, then stream in the milk and mix until incorporated. Add in the remaining flour and mix until combined. 
6. Evenly divide the batter between the cake pans and bake for about 28 minutes or until a toothpick inserted in the center of the cakes comes out clean. Cool on a wire rack for 10-15 minutes before removing the cakes from their pans.

For the Peanut Butter Marshmallow Filling

1. In a medium bowl, whisk together the peanut butter, marshmallow creme, milk, and cinnamon. Gradually whisk in powdered sugar.  

For the Peanut Butter Frosting

1. Combine the heavy cream and 1/4 cup of the confectioners' sugar in the clean bowl of an electric mixer fitted with the whisk attachment. Whip on medium-high speed until light, fluffy and stiff peaks form, being careful not to over mix.
2. Transfer the whipped cream to a separate bowl. In the now empty bowl fitted with the paddle attachment, combine the butter and peanut butter. Beat on medium-high speed until smooth, about 45 seconds.
3. Add the remaining confectioners' sugar to the bowl and mix in, slowly at first until incorporated, then increasing the mixer speed to high. Blend in the vanilla extract and salt, and continue to whip on high speed until very fluffy, about 4-5 minutes, scraping down the sides of the bowl as needed.
4. Use a large spatula to gently fold about a third of the whipped cream into the peanut butter frosting. Once the first addition has been evenly incorporated, gently fold in the remaining whipped cream until no streaks remain.

Assembly

1. When the cakes are completely cooled, split each cake into two layers.
2. Place the first layer on your cake plate or cake stand and cover with about 1/4 - 1/3 cup of the filling. Place the second layer on top and repeat this step until you get to the final cake layer, which you will place bottom-side down.
3. Cover the cake with a crumb coat and chill for 10 minutes in the freezer. Continue frosting the cake with the whipped peanut butter frosting.