1. Prepare Oven and Pan:

• Preheat your oven to 350°F (175°C).
• Line a 9×13-inch baking pan completely with parchment paper, allowing a slight overhang on the longer sides for easy lifting later. Grease the parchment paper lightly or spray with non-stick spray. Set aside.

2. Whip Eggs and Sugar:

• Separate eggs if preferred for maximum volume (whipping whites then folding in yolks later), or proceed as recipe implies: In a large bowl using an electric mixer (stand mixer with whisk attachment is ideal), beat the 4 large room temperature eggs together with the 1/2 cup granulated sugar on high speed.
• Continue beating for a full 5 minutes, until the mixture is very thick, pale lemon-colored, airy, and ribbon-like (when you lift the beaters, the batter falls back in a thick ribbon that sits on the surface briefly). (Adding 1 tsp vanilla extract here is common for sponge cakes).

3. Combine Dry Ingredients and Fold:

• In a separate medium bowl, sift together the all-purpose flour, unsweetened cocoa powder, baking powder, and salt. Whisk briefly to combine.
• Gently sift or sprinkle about half of the dry ingredients over the whipped egg mixture. Using a large rubber spatula, carefully fold the dry ingredients in until just barely combined (cut down the middle, scrape across bottom, fold over). Do not stir or beat!
• Sift or sprinkle the remaining dry ingredients over the batter and continue folding gently only until no large streaks of flour/cocoa remain. Be careful not to deflate the airy egg mixture.

4. Bake the Sponge Cake:

• Pour the batter into the prepared parchment-lined 9×13 inch pan.
• Gently spread the batter into an even layer using an offset spatula or the back of a spoon, being careful not to knock out the air.
• Bake for 12-15 minutes. The cake is done when the surface springs back lightly when gently touched. Do not overbake, as this will make it prone to cracking when rolled.

5. Roll the Warm Cake:

• While the cake is baking, prepare your rolling surface. Lay a clean, lint-free kitchen towel flat on your counter and dust it generously and evenly with the 1/4 cup of powdered sugar.
• As soon as the cake comes out of the oven, immediately invert the hot cake pan onto the prepared sugar-dusted towel.
• Carefully peel off the parchment paper from the bottom of the cake.
• Starting from one of the short sides of the cake, carefully and snugly roll the warm cake up with the towel inside the roll.
• Place the rolled-up cake (still in the towel) seam-side down on a wire cooling rack. Let it cool completely in this rolled position, at least 1 hour.

6. Make the Peanut Butter Filling:

• While the cake cools, make the filling. In a large, chilled bowl, whip the cold heavy cream with an electric mixer until soft peaks form.
• Add the sifted powdered sugar and the 1 tsp vanilla extract. Continue whipping until stiff peaks form.
• Add the smooth peanut butter and mix on low speed (or fold gently with a spatula) just until combined and smooth. Be careful not to overwhip at this stage.

7. Assemble the Roll Cake:

• Once the cake roll is completely cool, gently and carefully unroll it flat onto the towel.
• Spread the prepared peanut butter filling evenly over the surface of the unrolled cake, leaving about a 1/2-inch border along the edges.
• Sprinkle the chopped mini peanut butter cups evenly over the filling.
• Carefully re-roll the cake without the towel this time, starting from the same short side you started rolling from initially. Roll snugly but gently.

8. Garnish and Serve:

• Place the finished Chocolate Peanut Butter Roll Cake seam-side down on a serving platter.
• Dust the top generously with additional powdered sugar.
• Slice into rounds using a sharp serrated knife. Serve immediately or chill briefly before serving.