Preheat the oven to 350°F. Line a 12-cup muffin pan with cupcake liners. Line a second pan with 5 liners - this recipe makes about 17 cupcakes. Set aside.
Make the cupcakes: Whisk the flour, baking powder, and baking soda together. Set aside.
Using a handheld or stand mixer fitting with the paddle attachment, beat the room temperature butter on high until smooth and creamy - about 1-2 minutes. Add the sugar and beat on high speed for 2 minutes or until creamed together. Scrape down the sides with a rubber spatula as needed. Add the egg whites, vanilla extract1, butter extract2, and yogurt3. Beat on medium-high until combined. With the mixer on low speed, add the dry ingredients until just combined. With the mixer still on low, slowly pour in the milk4 until combined. Do not over mix. The batter will be slightly thick. Fold in the sprinkles5 but be careful and gentle as they can bleed color.
Spoon the batter into the liners filling only 1/2 full to avoid spilling over the sides. Bake for 17-19 minutes or until a toothpick inserted in the center comes out clean. Allow the cupcakes to cool completely before frosting.
Make the frosting: With a handheld or stand mixer fitted with the paddle attachment, beat the butter on medium speed until creamy - about 2-3 minutes. With the mixer on low, add 5 cups of powdered sugar, heavy cream, and vanilla extract. Increase to high speed and beat for 3 full minutes. Add up to 1/2 cup more confectioners' sugar if frosting is too thin or a Tablespoon of cream if frosting is too thick. Add a pinch of salt if frosting is too sweet.
Frost completely cooled cupcakes. I used the Wilton 8B piping tip. Start in the center of the cupcake and swirl upward. That's it! Top with additional sprinkles, if desired.
Make ahead tip: Cupcakes can be made up to 1 day in advanced, covered, and stored at room temperature. Cupcakes can also be frozen for up to 3 months in a airtight bag or container. Thaw overnight in the refrigerator.1I know pure vanilla extract has gotten pricier, but it is strongly recommended for the best flavor.2You can find butter extract with the other extracts in the baking and/or spice aisle. If you can't find it, no worries, you can leave it out.
3I use yogurt because I typically have it on hand— sour cream works well too.42% or whole milk is recommended, anything lower fat will change the texture.4For best results, avoid using nonpareils (those little balls) as they will bleed into the batter almost immediately. Just use plain old rainbow sprinkles or quins.