Preheat your oven to 350°F and line your muffin pan with cupcake liners. This ensures even baking and prevents the cupcakes from sticking.
Sift the cake flour, baking powder, baking soda, and salt together in a bowl. Whisking them well ensures an even rise and a tender crumb.
Beat butter and sugar until pale and fluffy. Then, add eggs and vanilla, mixing well for a smooth, airy batter.
Whisk buttermilk with part of the strawberry puree. Fold this mixture gently into the butter-sugar-egg batter until fully incorporated.
Fold in diced fresh strawberries carefully to keep them intact. Divide the batter evenly into the lined cupcake cups.
Bake until a toothpick inserted comes out clean, about 18-22 minutes. Let cupcakes cool completely before frosting.
Simmer fresh strawberry puree in a small saucepan over medium-low heat until thickened. Chill before adding to butter for frosting.
Whip butter until very pale and fluffy. Gradually mix in powdered sugar and reduced strawberry puree, then vanilla extract. Beat until smooth and creamy.
Place some diced strawberries in the center of cooled cupcakes. Pipe the strawberry buttercream around the strawberries for a beautiful finish.