CHOCOLATE CAKE

1. Preheat the oven to 350f/180c. Grease and line three six inch cake tins. 
2. In a small bowl, combine milk and lemon juice/vinegar. Set aside. In the bowl of a stand mixer fitted with the paddle attachment, cream butter and sugar until light and fluffy. Add vanilla and beat well. 
3. Sift flour, baking soda, baking powder and cocoa together in a bowl. With the mixer on low add one egg to the creamed butter and sugar mixture, followed by half of the flour mix, another egg, and the remainder of the flour mixture. Mix briefly, then pour in milk/lemon juice mixture. Beat until well combined. Scrape the bowl down well, add cider vinegar, and beat again. 
4. Divide the mixture between the three tins. Bake for 25-30 minutes, checking after 25, until a skewer inserted into the middle of a cake comes out clean. Allow to cool in their tins for 10 minutes, then turn onto wire racks and allow to cool completely.

DOUGHNUT SPRINKLES

1. Whisk meringue powder and water together in the bowl of a stand mixer. Add all of the icing sugar, and mix on low for 10-15 minutes until the icing is thick, white, and the consistency of cream cheese. Remove bowl from the stand mixer and add water a teaspoon at a time, mixing well between additions, until the icing is a pipeable consistency (I added about 6 teaspoons). You will need less water than you think! 
2. Add just over half of the icing to a bowl, and divide the remainder between as many small bowls as you would like to have glaze colours. (I made five glaze colours). Using a small drop of food colouring at a time, colour the larger bowl of icing light brown, and the remainder of the bowls your desired glaze colours. Mix well, and transfer each colour to a piping bag fitted with a small round tip (somewhere between a #2 and a #5)
3. Place your paper template on a baking tray, and place a piece of parchment paper over the top. I like to use magnets to secure both pieces of paper to the tray, to stop them from moving. Pipe circles of the light brown icing onto the parchment paper, followed by a layer of the "glaze" colour. Sprinkle each doughnut with sprinkles. (see GIF below). I like to pipe a whole tray of the base brown, then follow with two lines at a time of the glaze colour, stopping between lines to put on the sprinkles before the glaze dries out. Place in a safe place and leave until dry (3-4 hours, preferably overnight). Once dry, remove from paper and store in an airtight container. 

SWISS MERINGUE BUTTERCREAM

1.  In the bowl of stand mixer, combine egg whites, vanilla and sugar. Whisk briefly until combined. Place the bowl of the mixer over a small saucepan of water, taking care that the water does not touch the bowl. Turn the heat to medium. 
2. Whisking occasionally to prevent the egg white cooking, bring the egg mixture to 150f/65c. Place the bowl back onto the mixer, fitted with the whisk attachment, and whip on high speed until the mixture has doubled in volume and is completely cool. Feel the outside of the bowl with your hands - there should be no trace of heat left (this is especially important for the next step to ensure that the butter does not melt when you add it). Cooling may take up to 20 minutes. 
3. Once the bowl is cool, add the butter one chunk at a time. If the mixture looks curdled/melted, do not worry, just continue whipping, it will come together! Once all of the butter has been added, add vanilla, and mix on medium until smooth. Tint using gel food colouring if desired.

ASSEMBLY

1. Trim the top of each cake if required, to ensure a smooth level surface. Place the first layer of cake onto a cake stand or turn table, and place a large dollop of buttercream on top. Smooth using an offset spatula, and then place the second layer on top. Repeat the filling process until the cake is stacked. Smooth a layer of buttercream over the top of the cake, then crumb coat it with a very thin layer, before placing in the fridge for 30 minutes or so to set. Remove from fridge, and frost with a second, thicker layer of buttercream. Use a bench scraper or offset spatula to smooth the sides of the cake. 
2. Carefully arrange doughnut sprinkles on the outside of the cake. Chill well to allow icing to set, which will help the sprinkles stay in place.