Preheat oven to 325° F. Grease two muffin pans or line with paper liners and set aside.
In a medium bowl, combine the dry ingredients (flour [see note], baking powder, baking soda, and salt) and set aside.
In the bowl of a stand mixer, combine butter and sugar until light and fluffy, at least three minutes. Scrape down the sides of the bowl as necessary.
Add the egg whites one at a time, allowing each addition to incorporate before adding the next. Add vanilla bean paste (see note) and mix to combine.
With the mixer running on low, alternate additions of the dry ingredients and buttermilk. Add half of the flour, followed by half of the buttermilk. Repeat for remaining flour and buttermilk, allowing each addition to incorporate before adding the next.
Divide the batter between 15 muffin cups, filling each about ¾ full. Bake for about 20 minutes, turning the pan around after 10 minutes to help ensure an even bake. A toothpick inserted in the center of the cake should come out clean. Allow the cupcakes to cool completely on a wire rack.
For Jam:
Combine strawberries (see note), honey, lemon juice, and salt in a medium saucepan. Warm over medium-high heat, stirring often, until the mixture boils. Once boiling, reduce to a simmer and cook until thickened, about 20 minutes.
Remove the jam from the heat and stir in vanilla bean paste (see note). Allow jam to cool while you prepare the rest of the recipe. Mixture will thicken as it cools. Jam can be made ahead of time and stored in the refrigerator.
For Frosting:
Pulse the freeze-dried strawberries (see note) in a food processor until they are a fine powder. Set aside.
In the bowl of a stand mixer, combine the cream cheese and butter. Beat until smooth and creamy. Add the vanilla bean paste (see note), the strawberry extract (optional; see note), and salt and mix to combine.
Gradually add the sifted powdered sugar and mix until incorporated. Add the strawberry powder and mix until incorporated. If the buttercream is too thick you can add a little milk or heavy cream to thin it. If too thin, you can add a bit more powdered sugar until you reach the desired consistency.
For Assembly:
Using a small knife, cut a core from the center of each cupcake and fill with the cooled jam. Cut the bottom off of each core so that just the top surface remains. Place this piece of the core back on top of the jam to cover.
Frost each jam-filled cupcake. Top with fresh strawberries, if desired.Enjoy!
Notes
Note on cake flour: In a pinch you can substitute with all-purpose flour, your cupcakes just won't be quite as fluffy or tenderNote on buttermilk: I love using buttermilk in these cupcakes! That said, if you don't have buttermilk, you can do a quick substitution: put 1 teaspoon vinegar OR lemon juice into a liquid measuring cup, then add enough milk (I find that 2% milkfat or greater works best) to come up to the 1 cup line. Let sit for 5 minutes, then it's ready for use!Note on vanilla bean paste: You know me, it's in everything! I just adore this ingredient! If you'd prefer to substitute, you can use an equal measure of vanilla extract.Note on strawberries: I used fresh berries for the jam. Frozen berries will also work fine, the mixture will just take longer to boil (unless you thaw them first) and will likely take a little longer to thicken.Note on strawberry extract: For an added kick of strawberry flavor! This is optional, since the freeze-dried berries have such great flavor! If you don't have strawberry extract on-hand, just skip it. It will still be delicious!
Note on freeze-dried strawberries: You'll need one bag (typically 0.8-1.2 oz) of freeze-dried strawberries for this recipe. Make sure that you're using *freeze-dried* berries, as they're free of moisture and will process into a powder. Regular "dried" strawberries will not!