First, make the horn. Divide the fondant in half and roll it into long sausages. Place the sausages next to each other and wrap them together around the chopstick. Pinch them together at the top and gently squeeze to secure them to the chopstick. Place the horn on a plate lined with plastic wrap and allow to dry out while you decorate the cake.
Slice the bottoms off all cakes, removing any excess browning. Slice the tops off 2 of the cakes, leaving one cake rounded on top. Stack all layers, with the round layer on top. Carve the cake into a tall oval shape with a serrated knife. Spread some blue buttercream between each layer.
Coat the entire cake in a thin layer of buttercream. This is called a crumb coat and will help to trap any excess cake crumbs in this thin buttercream layer. Place the cake in the fridge for 20 minutes, for the crumb coat to stiffen.
Coat the cake in a thick, generous layer of blue buttercream. Draw the narwhal’s eyes and mouth with the black buttercream. Stick the pink candy melts onto the cake as blushing cheeks.
Place the remaining blue buttercream into a piping bag and snip off the end to create a large, round tip. Create the fins by piping a large dollop on either side of the cake, then dragging the downwards in a flicking motion. Repeat for the tail at the back of the cake.
Stick the horn into the forehead area and you’re done!