1/2 cup (115g) unsalted butter, softened to room temperature
1 cup (200g) granulated sugar
3 large egg whites, at room temperature
2 teaspoons pure vanilla extract2
optional: seeds scraped from 1/2 of a vanilla bean
1/2 cup (120g) full-fat sour cream3
1/2 cup (120ml) whole milk3
about 1/4 cup your favorite jelly (any flavor!)
Peanut Butter Frosting
5 Tablespoons (75g) unsalted butter, softened to room temperature
1 cup (250g) creamy peanut butter
1 cup (120g) confectioners' sugar
1/3 cup (80ml) heavy cream
1 teaspoon vanilla extract
¼ teaspoon salt
optional: crushed peanuts for topping
Preheat the oven to 350°F (177°C). Line a 12-cup muffin pan with cupcake liners. Line a second pan with 2 liners - this recipe makes about 14 cupcakes. Set aside.
Make the cupcakes: Whisk the cake flour, baking powder, baking soda, and salt together. Set aside.
Using a handheld or stand mixer fitted with a paddle attachment, beat the butter on high speed until smooth and creamy - about 1 minute. Add the sugar and beat on high speed for 2 minutes until creamed together. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. Add the egg whites, vanilla extract, and vanilla bean (if using). Beat on medium-high speed until combined, then beat in the sour cream. Scrape down the sides and up the bottom of the bowl as needed. With the mixer on low speed, add the dry ingredients until just incorporated. With the mixer still running on low, slowly pour in the milk until combined. Do not overmix. You may need to whisk it all by hand to make sure there are no lumps at the bottom of the bowl. The batter will be slightly thick.
Pour/spoon the batter into the liners - fill only 2/3 full to avoid spilling over the sides. Bake for 19-22 minutes, or until a toothpick inserted in the center comes out clean. For around 30 mini cupcakes, bake for about 11-13 minutes, same oven temperature. Allow the cupcakes to cool completely before filling and frosting.
Fill the cupcakes: Using a sharp knife, cut a circle/hole into the center of the cupcake to create a little pocket about 3/4 inch deep. Place about 1 teaspoon of jelly inside and top with the piece of cupcake you removed to seal it. See photos above for visual. Repeat with all cupcakes.
Make the frosting: Using a handheld or stand mixer fitted with a whisk attachment, beat the softened butter on medium speed for 1 minute until completely smooth and creamy. Add the peanut butter and beat on medium-high speed until the two are combined. Add the confectioners' sugar, cream, vanilla extract, and salt. Beat on low speed for about 20 seconds, then gradually increase to high speed. Beat on high for 1 minute. Frost the cupcakes. I used a Wilton piping tip #12 to frost.
Make ahead tip: Cupcakes can be made ahead 1 day in advance, covered, and stored at room temperature. Frosting can also be made 1 day in advance, covered, and stored in the refrigerator until ready to use. Leftover cupcakes keep well covered tightly in the refrigerator for 3 days. Frosted or unfrosted cupcakes can be frozen up to 2-3 months. Thaw overnight in the refrigerator.
If you cannot get your hands on cake flour, you can make a DIY version from all-purpose flour and cornstarch. Measure 1 cup of all-purpose flour. Remove 2 Tablespoons. Mix in 2 Tablespoons of cornstarch. This equals 1 cup of cake flour. I suggest doing this twice, mixing it all up in 1 bowl then removing 1/4 cup since you need 1 and 3/4 cups in this recipe.
For best flavor, pure vanilla extract is strongly recommended. If using imitation, increase to 1 Tablespoon (3 teaspoons).
Whole milk and sour cream are strongly recommended for the best taste and texture. A full fat plain yogurt would work instead, though the cupcakes may not be as light. Same goes with a lower fat milk. I suggest both of these ingredients are at room temperature so they mix easier into the batter.