Preheat oven to 350F (175C) and prepare a 12 count cupcake tin by lining with paper liners. Set aside.

Place your egg whites in a completely clean, dry, and grease-free bowl. Using an electric mixer, beat on high-speed until stiff peaks form.¹ Set aside.

In a separate bowl, use an electric mixer to beat together butter, oil, and sugar. Beat until ingredients are creamy and well-combined.

Scrape down the sides and bottom of the bowl and then stir in your vanilla extract and sour cream, stirring until combined.

In a separate bowl, whisk together your flour, baking powder, baking soda and salt.

Using a spatula and stirring by hand (don’t use your mixer or you run the risk of over-beating the batter), stir the dry ingredients into the wet (butter/sugar mixture) until completely combined. Scrape the sides and bottom of the bowl to ensure ingredients are well-combined. Set aside.

Using a spatula, gently fold your egg whites into your batter. While you do not want to over-mix this batter, it is important that the egg whites are completely combined. Use a gentle hand and stir until you can’t see any streaks of egg whites in the batter.

Divide batter evenly into prepared cupcake tin.

Bake on 350F (175C) for 17-19 minutes, or until a toothpick inserted in the center comes out mostly clean or with a few moist crumbs (no wet batter).

Allow cupcakes to cool completely before carving and frosting:

Once cupcakes have cooled completely, use a small knife to cut a hole about 1” in diameter and 1” deep into a cupcake (do NOT cut all the way down to the bottom, you are making a little nest for your sprinkles). Try to make the top of the hole slightly larger than the bottom. Remove this core/plug piece of your cupcake and then slice off the bottom so that only the surface of your cupcake (about ¼” thick) remains (see photo in post or video below for visual). Save this piece with the cupcake that you cut it out of so you can easily match each piece when you go to fill your cupcakes. Repeat with all remaining cupcakes.

Fill each cupcake cavity with sprinkles, filling just below the surface of each cupcake. Top with your cupcake plug that you reserved and gently press down.

Top cupcakes with frosting.

Feel free to use your favorite frosting with this recipe! I used my Swiss Meringue Buttercream for the cupcakes in these pictures (piped with an Ateco 848 tip) but will include more options below in the notes section.