Preheat oven to 180°C/350°F (160°C fan).

Cake pans: Grease and line the base of 2 x 15cm (6") cake pans that are 7.5cm (3") deep (Note 3 for other cake pan sizes).

Mix wet ingredients: Whisk together eggs, peanut butter, oil, honey and milk (small peanut butter lumps are ok).

Add dry ingredients: Stir in carrot. Add flour and baking soda, stir until just combined (over-mixing = hard cake = sad birthday pooch!)

Fill cake pans: Divide batter between cake pans, spread and smooth surface.

Bake: Bake 30 minutes or until skewer inserted into the centre comes out clean. Cool on racks.

Level and halve: Trim the mound off the top of each cake to make the tops flat. Then cut each cake horizontally in half using a serrated knife so you have four, even, flat cake layers. Frost per below.

Cook potatoes: Boil, steam or microwave potato until very soft.

Whip: Whip potato and yoghurt with an electric beater until fluffy and smooth as possible – about 1 1/2 minutes on medium speed (speed 5).

Adjust thickness: Use water as needed to loosen frosting to a soft, spreadable consistency (like human buttercream frosting). Use while warm – it "sets" and gets harder when it cools, Note 4.

White and blue frosting: Use uncoloured frosting to frost between cake layers and sandwich them. Keep remaining frosting to be coloured and used to frost the surface.

Mix ingredients in a small bowl, starting with 1 tablespoon milk. The frosting should be thin enough so it will spread quite smoothly on the top of the cake, but thick enough so the drips you make down the side will hold their form. (Do a test on a straight-walled glass). Adjust thickness with more cornflour / cornstarch (for thicker) or more milk (for thinner).

Sandwich layers: Place one cake layer on a turntable or serving platter. Spread with 3/4 cup white frosting. Top with another layer of cake, spread with 3/4 cup frosting, then repeat once more and top with the 4th cake layer.

Colouring frosting: Colour the remaining frosting blue using blue gel. To achieve the colour pictured, dip a toothpick into gel container and smear colouring on the surface of the potato. Dip a clean toothpick again into the gel and repeat (you need two dips to get enough colour into frosting). Mix frosting until colour is uniform.

Frosting surface with blue: Frost the top and sides of the cake with the blue frosting, spreading it as smoothly as you can.

Drip Frosting: Spoon 2 - 3 tablespoons of Drip Frosting on the top of the cake and spread carefully to the edge, ensuring you don't coax it over the edge. Now scoop up a teaspoon of the Drip Frosting and "drip" it down the side of the cake from the top edge. Repeat all around, making drips of different lengths.

Decorate: Decorate cake as desired with decorations that you want to stick to the frosting. I used silver, blue and white balls.

Set frosting: Immediately refrigerate for at least 3 hours to make the Drip Frosting set. (Also, the silver balls will sweat on the Drip Frosting unless it sets quickly). Keep refrigerated until ready to serve.

Happy birthday to your pooch!!!