Preheat oven to 180°C/350°F (160°C fan). Place oven rack in the middle to upper section of the oven. 

Place cupcake liners in a 12-hole muffin pan. Sift flour, cocoa and baking powder into a bowl and whisk to combine. In a separate bowl, beat butter and sugar with electric mixer until fluffy and pale. Add egg and beat until combined. Add vanilla, buttermilk, vinegar, and food colouring and beat to combine. Add dry ingredients and beat until combined. 

Fill the cupcake liners until about two thirds full and bake for approximately 20 minutes, until a skewer inserted in to one of the cupcakes comes out clean. Immediately transfer to a wire rack to cool.

Meanwhile, make the buttercream. Melt the white chocolate in short bursts in the microwave or using a double boiler. Set aside to cool. 

Beat butter and cream cheese together until smooth. While the mixer is running, gradually add the cooled melted chocolate and beat until combined. Add vanilla extract and icing sugar and beat on low speed until just incorporated, increase speed, and beat until fluffy, about 2 minutes. Refrigerate for approximately 30 minutes so that the mixture is firm enough to pipe. Pipe generously on to cupcakes. Top each cupcake with a Koko Black Raspberry Macadamia.