Marble Nutella Sponge Cake

Ingredients:
280g butter
1 tsp vanilla essence
(Beat butter & vanilla essence till light.  Weight 230g into a separate bowl & remaining in another bowl)

Plain Cake
160g cake flour
1/2 tsp baking powder
14 egg yolks ~ cold
3 egg whites ~ cold
20g sponge cake stabilizer/ovalette
200g caster sugar

Chocolate Cake
25g cake flour
15g cocoa powder
1/2 tsp baking powder
2 egg yolks ~ cold
1 egg whites ~ cold
50g caster sugar
8g sponge cake stabilizer/ovalette

Directions:

1. Preheat oven at 200 deg C (top bottom heat mode).  Prepare 2 cake tin of 9x2" square line the base with parchment paper.
2. Plain cake: Whisk eggs, sugar & ovalette till light & pale double in volume for about 10 mins.
3. Add 160g flour till thick & fluffy.  Fold in 230g butter in 3 portions till well combined.
4. Chocolate cake: Same process as the plain cake & fold in the remaining butter.
5. Scoop 150-200g of plain batter into each baking tings.  Spoon dollops of the chocolate batter & swirl slightly into the plain butter.  Repeat another round of this step, finishing both batters.
6. Bake for 10-13 mins.  When baked the top will look golden brown, dry to the touch & springs back when touch.  Cool cake onto cooling rack.  When cooled, sandwich cake with Nutella.