1-First Step: Get your pans and oven readyStart by preheating your oven to 350°F, which is 177°C. Line cupcake pans with paper liners and prepare two pans or bake in batches, since this recipe makes about 16 to 17 cupcakes. Having everything ready before mixing helps the batter stay airy and keeps the process smooth from start to finish.Take your butter, sour cream, milk, and egg whites out ahead of time so they can come to room temperature. This small step helps the batter blend better and gives the cupcakes a softer crumb. If you are baking for a party or school event, this recipe is easy to spread over a short prep window without feeling rushed.

2-Second Step: Mix the dry ingredientsIn a medium bowl, whisk together the cake flour, baking powder, baking soda, and salt. Whisking helps distribute the leavening evenly, which matters for an even rise. If your flour looks clumpy, give it a quick sift first.This is also the time to chop the chocolate sandwich cookies. You want small chunks, not fine crumbs, so you still get those nice cookies and cream bites inside each cupcake. Set the cookies aside so they are ready when the batter is mixed.

3-Third Step: Cream the butter and sugarIn a large bowl, beat the softened butter and granulated sugar on medium-high speed for about 3 minutes. The mixture should look pale and fluffy. This step helps trap air, which gives the cupcakes their light texture.Next, add the egg whites and beat on high speed for about 2 minutes until the batter looks smooth. Using egg whites only may seem unusual if you are used to whole eggs, but it helps the cupcakes stay tender and not heavy. The sour cream and milk bring back the richness that egg yolks would normally add.

4-Fourth Step: Add the wet ingredientsBeat in the vanilla extract and sour cream on medium-high speed until combined. The batter may look a little curdled at this point, but that is normal. Keep mixing until it comes together.Then pour in the whole milk slowly while mixing on low speed. A slow addition helps the batter stay smooth. If you see a few small lumps, use a whisk to gently break them up, but avoid over-mixing.

5-Fifth Step: Add the dry ingredientsWith the mixer on low, slowly add the dry ingredients. Stop as soon as the flour disappears. Over-mixing can make cupcakes tough, so this part should be gentle and brief. If needed, finish with a few turns of a whisk by hand.After that, fold in the chopped chocolate sandwich cookies with a spatula. Use a light hand so the cookies do not break down too much. You want bits of cookie throughout the batter for texture and flavor.

6-Sixth Step: Fill the liners and bakeSpoon the batter into the cupcake liners, filling each one about two-thirds full. This is important because it keeps the batter from spilling over the sides as the cupcakes rise. Since this recipe makes a fairly full batch, two pans or a second baking round may be needed.Bake for 19 to 22 minutes. The cupcakes are done when a toothpick inserted into the center comes out clean or with just a few moist crumbs. Let them cool in the pans for 20 minutes, then move them to a wire rack to cool completely before frosting.

7-Seventh Step: Make the vanilla buttercreamFor the vanilla buttercream, beat the softened butter until creamy. Add the confectioners’ sugar, cream, vanilla extract, and salt. Start on low speed so the sugar does not puff everywhere, then move to medium-high until the frosting turns light and fluffy.If the frosting feels too thick, add a small splash more cream. If it feels too soft, add a little more confectioners’ sugar. You want a texture that pipes well but still holds its shape on the cupcake tops.

8-Eighth Step: Make the chocolate buttercreamFor the chocolate buttercream, beat the softened butter until creamy, then add the confectioners’ sugar, cocoa powder, cream, vanilla extract, and salt. Mix on low first, then increase to high speed once the cocoa is incorporated. This helps keep the kitchen from getting coated in sugar and cocoa dust.Adjust the texture the same way you would with the vanilla version. Dutch-process cocoa is the best choice if you want a deeper chocolate color and a richer flavor that pairs well with the cookie pieces.

9-Ninth Step: Pipe the swirled frostingTo make the swirled look, place your piping tip inside a piping bag, then fold the bag over a tall glass. Fill one side with vanilla buttercream and the other side with chocolate buttercream. Remove the bag from the glass, press out air bubbles, twist the top, and pipe directly onto the cooled cupcakes.This method gives you the classic cookies and cream look without needing two separate piping bags. Finish with crushed chocolate sandwich cookies sprinkled over the frosting. If you want a thicker vanilla-only top, make a larger batch of vanilla buttercream, since the swirl amount is enough for the mixed topping but not as generous for one flavor alone.

10-Tenth Step: Serve and enjoyServe the cupcakes once the frosting is set. The recipe makes about 16 to 17 cupcakes, which is great for a birthday, bake sale, classroom treat, or weekend dessert. The blend of soft cake, cookie chunks, and creamy frosting gives each bite a nice mix of textures.If you have leftovers, cover them and keep them in the refrigerator for up to 3 days. Let them sit at room temperature for a short time before serving so the frosting softens a bit.