Place your large round pastry tip in your pastry bag and fill it with the white buttercream.
Pipe a flat round swirl on the cupcake.
Place the small pastry tip in the pastry bag and fill it with the black buttercream.
Pipe black swirl on the cupcake.
Using a tooth pick start in the center and drag the tooth pick out to the edge of the cupcake. Repeat around the whole cupcake seven to eight times.