Preheat the oven to 180°C (160°C Fan / Gas Mark 5), Grease and line 3 x 7" round cake tins. Place the butter and the sugar into a free standing mixer and beat together until smooth and pale in colour.
Add the eggs and Vanilla Extract and mix until mixture is smooth, scraping down the sides of the bowl as required. If the mixture begins to curdle add a spoonful of flour.
Sieve the flour on top and fold into the mixture until all the flour is combined.
Divide the mixture evenly between the three cake tins and place in the preheated oven. Bake for 30-35 minutes until the cake has risen and a skewer inserted into the centre of the cake comes out clean. Once baked allow to cool in the tins for 15 minutes and then place on a wire rack to cool completely.
Whilst the cakes are cooling make the buttercream.
Make sure your mixer bowl is clean and dry, place your egg whites and caster sugar into your clean mixer bowl and place the bowl over a pan of barely simmering water making sure the water doesn't touch the bottom of the bowl. With a balloon whisk stir the mixture until the sugar has dissolved - this will take about 5-10 minutes.
To check the sugar has dissolved rub some of the mixture between your fingers and it should be smooth. If you can still feel the sugar crystals continue to heat the mixture. Ensure the heat is low as you do not want the mixture to overheat.
Once the sugar has dissolved remove the bowl from the heat and place on your freestanding mixer with the whisk attachment. Whisk on a medium to high speed until the bowl is cold to touch and the meringue mixture forms stiff peaks - this should take about 8-10 minutes. It is important the mixture is completely cool before moving on to the next step.
Chop the butter into small cubes, on a medium mix speed add the cubes of butter one at a time into the meringue mixture. Once all the butter has been added turn the whisk speed up to high and whisk the buttercream until you have a glossy, smooth buttercream - the buttercream may curdle once all the butter has been added don't worry if this happens, whilst mixing on a high speed the buttercream will come together.
Add the Vanilla Extract into the buttercream and mix through. Add a few drops of Pink Food Colour Gel into the buttercream and whisk through adding a few more drops until you have a light pink buttercream.
Flatten the top of each layer of cake, do this by cutting any domed tops off each cake.
Place a small blob of buttercream onto your cake board or serving plate.
Place a cake layer on top. Place a few spoonfuls of buttercream onto the cake layer and smooth out using a palette knife, place another cake layer on top and repeat until all cake layers have been added. Now crumb coat your cake by smoothing buttercream around the edge and on top of the cake. This should only be a thin layer of buttercream so you should be able to see the cake sponge through some areas of buttercream. To create a smooth finish run a large palette knife dipped in boiling water around the edge and the top of the cake.
Place the cake in the fridge for 30 minutes to chill and allow the crumb coat to set.
Whilst the cake is chilling place a third of the remaining buttercream into a separate bowl and add a few more drops of the Pink Food Colour Gel and mix until you have a darker pink colour.
Once the cake has chilled remove from the fridge and using your light pink buttercream smear a ring of buttercream around the edge of the cake about 6cm high, using a palette knife to smooth the buttercream.
Pour the Sprinkles into a bowl and using your hand pat the sprinkles onto the buttecream ring to cover completely in sprinkles.
Place the light pink buttercream into a piping bag and cut the end of the piping bag to make about a 1cm hole. Pipe ring of light pink buttercream around the top of the sprinkle band and then continue up the sides and top of the cake. Repeat for the dark pink buttercream piping a ring of buttercream around the bottom edge of the sprinkle band and then to the base of the cake. It is important the buttercream layer is quite thick.
Use a large pallet knife to smooth the buttercream around the edges and on top of the cake, this should create the uneven faultline around the sprinkles.
Place a small amount of gold paint into a bowl and using a small paint brush, paint around the edge of the faultline to define the line.
Your Rose Gold Faultline Cake is now ready to serve and enjoy!