Prepare Strawberry Jam: In a medium pot, combine quartered fresh strawberries with granulated sugar and lemon juice. Cook over medium heat for about 15–17 minutes, stirring occasionally, until thickened. Let cool completely.

Make Cupcake Batter: In a large bowl, whisk together cake flour, baking powder, baking soda, and salt. Cream softened unsalted butter and sugar together until light and fluffy. Add in egg whites and vanilla, then alternate adding dry ingredients and buttermilk until smooth.

Bake Cupcakes: Preheat oven to 350°F (175°C). Line a cupcake pan with liners and fill them two-thirds full with batter. Bake for 16–18 minutes or until a toothpick comes out clean. Cool in the pan for 10 minutes before transferring to a wire rack.

Prepare Frosting: Whip softened butter until pale and creamy. Gradually add cold cream cheese and powdered sugar, mixing on low speed. Fold in ground freeze-dried strawberries.

Assemble Cupcakes: Core centers from cooled cupcakes and fill with strawberry jam. Pipe frosting on top, creating a swirl and garnish with fresh strawberries if desired.