Preheat the oven to 180C / 350F / 160C fan forced. Grease and line 3 x 8 inch cake tins with baking paper.
Sift together the flour, baking powder and salt, mix, then set aside.
Beat together the butter and sugar. Add the egg whites and vanilla beat until it looks light and fluffy. It may look split but that’s ok. (about 3 minutes).
Add half the dry ingredients and mix through with a spatula until just combined. Now add the milk and gently mix through followed by the remaining dry ingredients. Mix with a spatula until just combined as overmixing will give you a dense cake.
Divide the batter evenly among the cake tins and very gently nudge it to the edges and level it out. Make sure not to knock all the air out of it.
Bake for 25-27 minutes. Do not open the oven door before 20 minutes or the cakes may sink.
Remove from the oven and allow them to cool in the tins for 5 minutes before turning out onto cooling racks.
FOR THE MARSHMALLOW FROSTING
Place the egg whites, sugar and cream of tartar into a heatproof glass bowl and sit it on top of a saucepan of simmering water - make sure it is not touching the water.
Use a handheld beater to beat the mixture for 5-6 minutes, until it becomes very thick and holds it's shape when moved. If you have a candy or meat thermometer, check the temperature is at 60C / 140F - at this temperature the eggs are pasteurized.
Remove the bowl from the saucepan and turn off the heat. Continue to beat the frosting for a further 5 minutes until it has cooled almost to room temperature and is even thicker and glossy. It should be at stiff peak stage.
Beat in the vanilla extract.
TO MAKE THE GANACHE
Place the chocolate in a bowl. Heat the cream in a small saucepan until it starts to bubble then pour it over the chocolate. Let it sit for about 2 minutes to melt a little then stir it together into a smooth ganache.
TO ASSEMBLE THE CAKE
Spread the jam over two layers of sponge.
Place the first layer onto your cake plate and top it with the marshmallow frosting to nearly an inch deep but leave a gap of about 2cm from the edges.
Sit the second layer and push down lightly to spread the marshmallow frosting a little bit more. Add some more frosting on top of this layer going nearly all the way to the edge.
Sit the third layer on top and press down lightly.
Pour the ganache over the top and use an offset spatula to very carefully push it towards the edges to so it can drip down.
Transfer the remaining frosting to a piping bag and pipe little swirls all around the top.
Cut 7 mini wagon wheels in half and sit them on top of the swirls all the way around. Add the last whole mini wagon wheel to the centre of the cake, pipe a swirl on top, then sit another half on top of it.
I use a standard Australian 20ml tablespoon (4 teaspoons worldwide)
For best results you should always weigh ingredients like flour and sugar. Kitchen scales like these are relatively cheap but if you can’t weigh the ingredients, use the spoon and level method (don’t scoop).
TOOLS USED IN THIS RECIPE
A sugar thermometer is not absolutely necessary, but very handy when making the frosting
3x 8 inch round cake tins
A handheld beater can get this job done
I always use a silicone spatula to get as much batter as possible