A home baker marked Alex's birthday this past weekend by adding a chocolate peanut butter layer cake to a long-running rotation of chocolate desserts, according to a first-person account of the cake. The cake's full name is Sour Cream-Chocolate Cake with Peanut Butter Frosting and Chocolate Peanut Butter Glaze, though the account notes it is actually made with cream cheese peanut butter frosting.
The dessert fits a pattern the author describes in the birthday requests: chocolate with caramel, toffee, coffee, hazelnut cream, Oreos, raspberries, white chocolate, dulce de leche, banana cake, and a chocolate cheesecake with brownie chunks. 
The recipe comes from the cookbook Sky High, which the author has used before for a Pistachio Petit-Four Cake and for the vanilla and chocolate cakes in a wedding cake project. 
What the cake combines
The cake layers are sour cream-chocolate. Between and over them are a cream cheese peanut butter frosting and filling, plus a chocolate peanut butter glaze. The author writes that the combination of cream cheese and peanut butter initially seemed questionable but worked because the tangy and salty notes of the cream cheese balance the peanut butter.
Why the cookbook mattered
The author recommends Sky High for bakers interested in celebration cakes, citing recipes such as blue cornmeal with caramel cream, gingerbread beer with bittersweet chocolate, and bananas with praline and white chocolate. Another practical point: many of the cake recipes are one-bowl, and the author mixed the chocolate peanut butter cake with a whisk rather than an electric mixer. 
The account does not include measurements, baking times, or a full ingredient list, so readers looking to replicate the cake would need the original cookbook. The cake was made for a birthday, and the author notes the previous year's dessert was a Brownie Mosaic Cheesecake.
Editorial Notes