Yield: about 16 servings

Ingredients

For the cake:

  • 1¾ cups plus 2 tbsp. (9 3/8 oz.) all-purpose flour
  • 1½ cups (4½ oz.) unsweetened cocoa powder, plus more for dusting the pans
  • 1 tbsp. instant espresso or coffee powder
  • 1½ cups boiling water
  • ¾ cup sour cream
  • 1 tbsp. vanilla extract
  • 1½ cups (3 sticks) unsalted butter, at room temperature
  • 2½ cups plus 2 tbsp. (18 3/8 oz.) sugar
  • 3 large eggs, at room temperature
  • 1¼ tsp. baking soda
  • ¾ tsp. salt

For the filling and frosting:

  • ¾ cup heavy cream, chilled
  • 3¼ cups confectioners’ sugar, sifted, divided
  • 1½ cups (3 sticks) unsalted butter, at room temperature
  • 1 cup creamy peanut butter
  • 1 tbsp. vanilla extract
  • Pinch of coarse salt

To garnish:

  • Mini peanut butter cups, halved
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  • step 1: HideShow Images

    To make the cake, preheat the oven to 350˚ F.  Butter the edges of 3 8-inch round cake pans and dust with cocoa powder, shaking out the excess.  Line the bottoms of the pans with parchment paper.  In a medium bowl, combine the cocoa powder, espresso powder, and boiling water.  Whisk until smooth; set aside to cool slightly.  When cooled down a bit, whisk in the sour cream and vanilla.  Set aside.  In the bowl of an electric mixer, beat the butter on medium-high speed until smooth, about 1 minute.  Gradually blend in the sugar and whip on medium-high speed until light and fluffy, 2-3 minutes more.  Blend in the eggs one at a time.  In a medium bowl, combine the flour, baking soda, and salt; whisk to blend.

  • step 2: HideShow Images

    With the mixer on low speed, add the dry ingredients in three additions alternating with the sour cream mixture, beating each addition just until incorporated.  Divide the batter evenly between the prepared pans.  Bake the cake layers for about 30-32 minutes or until a toothpick inserted in the center comes out clean, rotating the pans during halfway through to ensure even baking.  Transfer the baked cake layers to a wire rack and let cool in the pans at least 30 minutes before inverting onto the rack to cool completely.

  • step 3: HideShow Images

    To make the filling and frosting, combine the heavy cream and ¼ 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.  Transfer the whipped cream to a separate bowl.  In the now empty mixer bowl fitted with the paddle attachment, combine the butter and peanut butter.  Beat on medium-high speed until smooth, about 45 seconds.  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.  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.

  • step 4: HideShow Images

    To assemble the cake, place one of the cake layers on a cake board or serving platter.  Spread an even layer of the frosting over the top of the cake.  Top with a second cake layer and another layer of the frosting.  Place the final cake layer on top.  Frost the top and sides of the cake using a thin crumb coat at first.  Place in the freezer for 30 minutes to set.  Reserve about 1 cup of the remaining frosting in a pastry bag fitted with a decorative tip (I used a Wilton #21).  Once the crumb cake is set, frost the top and sides of the cake again using an offset spatula for a smooth finish.  Use the reserved frosting to pipe a border around the base of the cake.  Pipe swirls evenly around the top border of the cake.  Finish by garnishing with halved peanut butter cups.  (I find that freezing the candy for an hour or so beforehand helps them unwrap and cut while still looking nice.)  Refrigerate the cake until ready to serve.

  • step 5: HideShow Images

    Notes:
    To make the cake in two 9-inch pans, reduce the amount of batter by one third.
    To make the cake in three 9-inch pans, increase the amount of batter by one third.
    The baking times for alternate sizes may differ, so use the toothpick test to monitor doneness.

    For tips on frosting your cake, see this post about crumb coats and this about smoothly frosting a cake.  Also, I think this revolving cake stand is invaluable.