Prepare Cupcakes:
Preheat oven to 350°F (175°C) and line a 12-cup muffin pan with cupcake liners.
Mix Dry Ingredients:
In a medium bowl, whisk together flour, baking powder, and salt. Set aside.
Cream Butter and Sugar:
In a large mixing bowl, beat butter and sugar until light and fluffy, about 3–4 minutes.
Add Eggs and Vanilla:
Beat in eggs one at a time, then add vanilla extract.
Combine Wet and Dry Ingredients:
Alternately add flour mixture and milk to the butter mixture, beginning and ending with flour. Fold in strawberry puree gently.
Bake:
Divide batter evenly among cupcake liners. Bake for 18–22 minutes, or until a toothpick inserted into the center comes out clean. Cool completely on a wire rack before frosting.
Prepare Strawberry Meringue Buttercream:
In a heatproof bowl over a simmering pot of water, whisk egg whites and sugar until sugar dissolves and mixture reaches 160°F (71°C). Remove from heat.
Using a stand mixer, whip egg white mixture until stiff, glossy peaks form and cooled to room temperature.
Gradually add softened butter, beating until smooth. Mix in salt, vanilla, and strawberry puree. Adjust consistency with more puree if needed.
Frost Cupcakes:
Pipe or spread the strawberry meringue buttercream over cooled cupcakes. Decorate with fresh strawberry slices if desired.