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

Grease and line the base of 2 x 20cm/8" cake pans.

Whisk together eggs, peanut butter, oil, honey and milk (little peanut butter lumps ok).

Stir in carrots. Then add flour and baking soda, stir until just combined (over mixing = hard cake = sad birthday pooch).

Divide batter between the cake pans, spread and smooth surface.

Bake 25 minutes or until skewer inserted into the centre comes out clean.

Cool on racks. Frost per below.

Boil, steam or microwave potato until very soft.

Whip potato and yoghurt with an electric beater until fluffy and smooth as possible (won't go 100% smooth) - about 1 1/2 minutes on medium speed (speed 5).

Use water as needed to loosen frosting to soft spreadable consistency (like human buttercream frosting!). Use while warm (it "sets" when it cools).

Spread 1/4 frosting on one cake.

Top with other cake. Frost tops and sides with remaining frosting, reserving some to pipe decorations if desired (3/4 cup frosting).