2) Remove the saucepan from the heat and stir in the butter and bicarbonate of soda. Working quickly, spread the mixture onto the greased baking sheet. Allow to cool slightly before using a spatula to spread the mixture out even further.
3) Once cooled a little more, stretch the brittle out very thin by hand. Once fully cooled, approximately 30 minutes, break the brittle into small pieces. You will not need all this brittle for the cupcakes, the extra can be stored in a plastic storage container for snacking or a second batch of cupcakes.
For the buttermilk cake:
1) Preheat the oven to 180C/Gas 4. Grease a baking sheet with nonstick spray. Line the cups of 3 cupcake or muffin tins with paper baking cases.
2) In a large bowl, beat together the sugar and butter until smooth. Add in the eggs and yolks, 1 at a time. Scrape down the bowl and mix after each egg addition.
3) In a separate bowl, sift together the cake flour, plain flour, baking powder, salt and bicarbonate of soda. In a third bowl, mix together the buttermilk and vanilla essence.
4) Add the dry ingredients and the buttermilk mixture to the butter-egg mixture, alternating between the dry and wet ingredients. Fold in the chopped peanut brittle.
5) Using a medium-size ice cream scoop, scoop the batter into the prepared cupcake cases. Add a layer of mini chocolate shell candies. Bake until the tops of the cupcakes lightly spring back when pressed and a toothpick inserted in the centre comes out clean, about 20 to 22 minutes. Allow to cool.
6) Fill the cooled cupcakes with the butterscotch caramel. Spread the fudge icing on top. Sprinkle the caramel popcorn over the icing and top with a dollop of the vanilla buttercream. Top the buttercream with a mini chocolate shell candy.
For the butterscotch caramel:
1) Warm the butterscotch topping, and then add the cream and salt, mixing until smooth. Allow the mixture to cool, and then transfer to a disposable pastry bag fitted with a small tip and use to fill the cupcakes.
For the fudge icing:
1) In a food processor, blend the butter, sugar, cocoa and salt until smooth. Add the golden syrup and vanilla essence. Blend again, making sure to scrape the sides of the bowl.
2) Add the chocolate and pulse until completely combined. It should be smooth and creamy.
For the caramel popcorn:
1) Place the brown sugar, salt, butter, golden syrup and vanilla essence into a microwave-safe container, and cook on high power for 1 minute. Remove and stir until smooth. Place the container back in the microwave and cook again for another 2 minutes, or until the mixture is bubbling.
2) Remove the container from the microwave and stir in the bicarbonate of soda. It will foam up.
3) Spray a large stainless steel bowl with nonstick spray, and place the popcorn in it. Pour the hot mixture from the microwave over the popcorn, and toss until evenly coated. Spread the popcorn over a sheet tray and move it around until it is all separated. Allow the mixture to cool before layering on top of the fudge icing.
For the vanilla buttercream
1) In a bowl, whisk together the egg whites and sugar. Heat them over a bain marie or a saucepan of boiling water until hot and the sugar is melted.
2) Pour the hot egg white-sugar mixture into the bowl of an electric mixer and whisk on high until the mixture is cooled. Switch to a paddle attachment. With the mixer running on medium-high speed, gradually add the softened butter until the frosting is thick, smooth and glossy. Add the vanilla essence, and mix until combined.