Today is my 34th birthday!It’s been a really fun one so far: my little sister is visiting, I made this Sicilian pizza, went to dinner and to see Golden Girls Live! with a bunch of friends, did some vintage shopping, and saw Rocketman last night. Pretty great, right?!Now it’s time to talk birthday cake. I make many (many many many) throughout the year, but this one is mine: Peanut Butter Marble Cake, y’all!We’re talking thick layers made with my favorite peanut butter batter and swirled with dark chocolate a la Marble Bundt Cake. Yesssss.The cake is filled and frosted with a silky Chocolate-Peanut Butter Buttercream. This stuff is sweet-salty magic and it swoops like a dream!All that, and I didn’t even mention all the chopped peanut butter cups in the middle! There are even more on top 😊 It’s a total showstopper—the ultimate chocolate-peanut butter cake, as far as I’m concerned.I can’t think of a more delicious way to start my 35th trip around the sun 🎉

Peanut Butter Marble Cake
makes one 2-layer 9-inch round layer cake

Cake Batter:
2 2/3 cups all-purpose flour
1/3 cup cornstarch
1 teaspoon baking powder
1/2 teaspoon baking soda
1/2 teaspoon Kosher or sea salt
1/2 cup (1 stick) unsalted butter, softened to room temperature
1 1/2 cup creamy-style peanut butter*
1 1/2 cups light brown sugar, packed
1/2 cup granulated sugar
4 large eggs, room temperature
1 tablespoon pure vanilla extract
1 1/2 cups buttermilk
4 ounces dark chocolate

Chocolate-Peanut Butter Buttercream:
1 cup unsalted butter, softened to room temperature
3/4 cup creamy-style peanut butter
3 cups confectioners sugar
2/3 cup cocoa powder
pinch of salt
2 teaspoons pure vanilla extract
1/3 cup heavy cream

For assembly:
12 miniature peanut butter cups + more for topping

Preheat oven to 350F. Grease 2 9-inch round cake pans. Line with parchment and grease again. Set aside.

Make the cake batter. In a medium mixing bowl, whisk together flour, cornstarch, baking powder, baking soda, and salt. Set aside.

In a large mixing bowl, use an electric mixer to beat butter and peanut butter until combined and fluffy. Beat in light brown and granulated sugars. Add eggs one at a time, followed by vanilla. Mix in half the dry ingredients followed by half the buttermilk. Add remaining dry ingredients, followed by remaining buttermilk. Set aside.

Place chocolate in a microwave-safe bowl. Heat in 30 second increments in the microwave, stirring in between, until melted. This may also be done in a double boiler.

Transfer 1 1/2 cups of batter into the bowl with the melted chocolate. Use a fork and/or silicone spatula to combine the two.

Divide remaining peanut butter batter among prepared pans. Tap full pans on the counter five times to release any large air bubbles. Dollop chocolate batter over the tops and use a thin knife or skewer to lightly marble it in. Bake 40-42 minutes, or until a toothpick inserted in the centers comes out clean.

Let cakes cool in the pans for 15 minutes. Run a thin, flexible knife around the edges. Invert cakes onto a cooling rack and let cool completely.

Make buttercream. In a large mixing bowl, use an electric mixer to beat butter until light and fluffy (about two minutes). Beat in peanut butter. Add in confectioner’s sugar in two installments, followed by cocoa powder and salt, scraping down the bowl as necessary. Add in vanilla, followed by heavy cream. Beat on high for 1-2 minutes, until very fluffy.

Place 12 miniature peanut butter cups on a cutting board. Use a large, sharp chef’s knife to cut them into small pieces (I like to cut them into eighths).

Use a serrated knife to even out the tops of the cake layers. Place one cut-side-up on a serving plate or cake stand. Top with a thin layer of buttercream, followed by chopped peanut butter cups. Top with the second layer cut-side-down. Frost and decorate cake. Garnish with more peanut butter cups, if desired.

Slice and serve. Leftovers will keep covered at room temperature for up to two days or in the refrigerator for up to five. If storing in the refrigerator, let cake sit at room temperature for 30 minutes before serving. Cake is best served at room temperature.