Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with cupcake liners.

In a medium bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt.

In a separate large bowl, combine vegetable oil, buttermilk, egg, red food coloring, vanilla extract, and white vinegar. Whisk until smooth.

Gradually add the dry ingredients into the wet mixture, stirring gently until just combined.

Divide the batter evenly between the cupcake liners, filling each about two-thirds full.

Bake for 18–20 minutes or until a toothpick inserted into the center comes out clean.

Allow cupcakes to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.

Beat the softened butter in a large mixing bowl until creamy and smooth.

Gradually add the powdered sugar, one cup at a time, mixing until incorporated.

Add vanilla extract and a pinch of salt, then slowly beat in the heavy cream.

Increase speed to high and beat until light and fluffy.

Once cooled, use a piping bag fitted with a star tip to pipe a swirl of frosting onto each cupcake.

Place a fresh raspberry on top of each frosted cupcake and tuck a small rosemary sprig beside it.

Dust lightly with powdered sugar.