Rainbow Cake
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19 oz or (275g) unsalted (sweet) butter
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1 cup granulated or caster sugar
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7 large eggs
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1 teaspoon pure vanilla extract
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4 cups (400g) sifted cake flour (to make cake flour, place 2 tablespoons cornflour in a 2 cup measuring cup and top fill up the rest with plain flour)
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2 teaspoons (10g) baking powder
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1/2 teaspoon (3g) salt
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Food colouring gels in: Royal Blue, Violet, Sky Blue, Green, Yellow, Orange and Red
To decorate
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Fondant in the colours of your choice
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Mini white marshmallows
Step 1 - Preheat the oven to 325°F/160°C and put a rack in the centre. Butter and line a 21cm round springform pan. Weigh the bowl of your electric mixer and record the weight-this is important.
Step 2 - Beat the butter and sugar in an electric mixer until light and fluffy, about 2 minutes. Beat in the eggs one at a time, mixing well-it may look curdled but it's ok, it will come together once you add the flour. Then add the vanilla extract. Stir in the flour mixture and baking powder at low speed until just combined.
Step 3 - Now comes the tricky part. Get your food colouring and get 7 bowls or containers. Figure out how much your batter weights. To do this, you weigh the bowl with the batter and subtract the weight of the bowl that you recorded. Mine weighed about 2 kgs (4 pounds). Divide into seven which was just less than 300grams/10.6 ozs per container. The last colour that put in it will dominate so gradually put a little less for the last colour (which for me was red). I started with 280grams for the Royal Blue and ended up with about 220grams for the red.
Step 4 - Take your lined pan. place a circle of the royal blue batter in a circle shape. Then in the centre of this place another circle of batter of the Violet. Keep doing this with the rest of the colours until you reach the last colour red. My dough was a bit too thick so I pressed it down with a sheet of parchment so that it reached the sides. Place it in the oven being careful not to tip the tin sideways.
Step 5 - Bake until a toothpick inserted into the centre comes out clean, about 55-60 minutes. Cool in the pan 10 minutes and then cool.
Vanilla Buttercream
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125g/4 ozs butter, soft at room temperature
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3 cups icing sugar, sifted
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2 tablespoons milk
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vanilla extract
Step 1 - Beat butter in an electric mixer fitted with a paddle attachment. Gradually add the icing sugar 1/2 cup at a time along with milk to help it bind. Beat for about 5 minutes on medium to high speed. Add vanilla extract and beat until incorporated. Spread onto cooled cake.
To assemble
Step 1 - Roll each fondant colour into a long sausage shape and then flatten out with a small rolling pin. With a sharp paring knife or a pizza cutter, trim it to make a rainbow shape and place on cake.