Prepare Cupcake Batter: In a bowl, whisk together flour, baking powder, and salt. In a separate bowl, cream together butter and sugar until light and fluffy. Beat in eggs, one at a time, and vanilla extract. Gradually add dry ingredients and milk, alternating between the two, beginning and ending with dry ingredients.

Prepare Raspberry Swirl: In a blender, puree raspberries and sugar until smooth. Strain to remove seeds.

Swirl Batter: Fill cupcake liners with batter until halfway full. Drop a small spoonful of raspberry puree onto each cupcake and use a toothpick to gently swirl it into the batter.

Bake: Bake in a preheated oven at 350°F (175°C) for 18-20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean.

Prepare Frosting: In a bowl, beat the softened butter and vanilla extract until creamy. Gradually add powdered sugar, beating until smooth and fluffy. Divide the frosting into two portions. Mix 2 tablespoons of raspberry puree and vanilla extract into one portion of the frosting. Keep the other portion white. If desired, add natural red food coloring to the raspberry frosting until the desired shade of red is achieved.

Swirl Frosting: Place both colors of frosting side by side in a piping bag fitted with a large star tip. Gently squeeze the bag to pipe the red and white frosting in a swirl onto each cupcake.