Preheat your oven to 180°C [350°F] or 160°C fan. Grease and line two 6 inch cake round cake tins. If needing to, trace the image for your buttercream transfer now and set aside (pen is clearer than pencil). See the Top Tips section above for guidance if you don’t have access to a printer.

In a large bowl, cream together the butter and sugar until light and fluffy.

Add in the eggs, beating in one at a time.

Sprinkle in the zest and beat in until evenly distributed.

Sieve in the flour and mix in until no flour is visible. Avoid over mixing here.

Split the mixture evenly between the two tins and tap them a couple of times on the counter to pop and air bubbles hiding in the mixture.

Bake on the middle shelf for 40 - 45 minutes (these are thick cake layers!). This will depend on how hot your oven runs and can take less or more time, so check after 35 minutes.

While your cakes are baking, make the buttercream for your transfer.

Turn the sheet of baking parchment/greaseproof paper that you have traced on over so that the pen is facing down. Place it on a baking tray and tape the paper to the tray to prevent slippage while you pipe.

In a large bowl, beat the butter to loosen it. Add ½ the icing sugar and beat in until fluffy. Add the other ½ and beat in until fully incorporated.

Squeeze in the juice and beat in until smooth. Add the milk and beat in until the buttercream is creamy and a little softer. The milk simply makes the buttercream easier to work with.

Spoon roughly 1 tbsp into a smaller bowl. Repeat this for another 2 bowls, then ½ tbsp in another bowl.

Leave one bowl free of food colouring. Add the brown food colouring to one bowl and mix in until an even colour is achieved. Add a tiny amount of black food colouring to another bowl and mix in to achieve a shade of grey. Lastly, add the pink food colouring to the bowl of ½ tbsp buttercream.

Add the grey buttercream to a piping bag/sandwich bag with a very small amount of the end snipped off. Trace around the image outline using the grey buttercream.

Place the tray in the freezer to harden the buttercream outline. Spoon the rest of the different tinted colours into separate piping bags/sandwich bags with a very small amount of the ends snipped off.

Retrieve the tray from the freezer and outline the rest of Appa’s features using the different colours before filling them in. Use a cocktail stick to carefully spread the buttercream into the hard to reach places like the fur above his eyes.

Use a cutlery knife or small palette knife to smooth over the surface of the filled areas very gently. Place back in the freezer for now.

Add the sky blue food colouring to the rest of your buttercream in the large mixing bowl and beat in until your desired colour is achieved.

Spoon some of this blue buttercream into a piping bag. Retrieve your tray from the freezer again and pipe the blue buttercream around the outline of your Appa. This creates stability and allows for better blending when the transfer is complete.

Pipe the blue buttercream over the entire image and gently smooth over with your palette or cutlery knife again to make sure that Appa will lay flat.

Place your buttercream Appa in the freezer again and leave in there until it is firm to the touch.

Your cake sponges should now be about ready. You will know this when a skewer or cocktail stick comes out clean when tested, the surfaces bounce back when gently pressed on, and you hear little to no crackling/bubbling when you listen to them.

Once baked, allow your sponges to cool in the tins for 10 or so minutes before transferring upside down to a wire rack to cool completely.

While your cakes are cooling, make your white chocolate shards. Line a baking tray with baking parchment/greaseproof paper.

Split the chocolate evenly into four heatproof bowls. One at a time, temper the chocolate in the microwave following the proceeding steps. This is ideal but not essential.

Take around ⅓ of the chocolate out of the first bowl and put it aside for now. Melt the remaining chocolate in the microwave in 20 second bursts, stirring in between until melted. Once completely melted, add the ⅓ you took out earlier piece by piece, stirring until it has melted in the warm chocolate. This brings the temperature of the chocolate back down.

Place the bowl back in the microwave for 10 seconds.

Repeat steps 5 and 6 with the three other bowls, adding the blue, red and green food colouring into separate bowls once tempered. Leave the first bowl of tempered chocolate free of colour as this will be the chocolate that represents air bending.

Spoon the chocolate onto the lined tray, spreading and swirling however you wish. Be mindful that the more your spread and swirl, the more the colours will blend into one and will be hard to differentiate!

Place your chocolate in the fridge while you decorate your cake.

Using the remaining blue buttercream, stack and decorate your cake. If needed, carefully cut and remove the top of your cake sponges if they have domed.

Place a small dab of buttercream onto your plate/cake board/cake stand and place your first layer on top of it.

Spoon a generous amount of buttercream on the top of the cake layer and spread it out evenly. Place the second and last sponge layer on the top.

Cover the entire cake with the remainder of your blue buttercream. This doesn’t have to be perfectly smooth! But, if you are aiming for a smooth finish, make sure to do a thin (crumb) coat of buttercream first. Then, chill for 10 or so minutes in the fridge, then smooth over the remaining buttercream using a cutlery or palette knife until smooth.

Retrieve your Appa transfer from the freezer. Remove the tape and carefully lift the paper from the tray. Fold the paper in half if needed, then turn your buttercream Appa upside down onto the top of your cake with the paper facing up. Gently peel the paper away from your buttercream transfer.

If needed, heat a teaspoon under some hot water, dry it off and then use the tip to gently smooth any areas on the buttercream transfer. If doing so, remember to wipe it clean in between colours.

Use the black food colouring and the red food colouring/paint to paint or dab on any features like Appa’s eyes, nose and tongue detail.

Use any remaining buttercream to pipe “YIP YIP” around Appa’s face if desired.

Retrieve the chocolate from your fridge. Carefully break it into well sized shards and press them into the buttercream around the edge of the cake.

Chill until ready to serve.