150gcaster (superfine) sugar (divided in half)(3/4 cup / 5.3oz) (notes)
35gcornflour (cornstarch)(1/4 cup / 1.2oz)
226gunsalted butter, room temperature(1 cup / 2 sticks)
12 hole muffin tin or silicone muffin tin
FOR THE VANILLA CUPCAKES
Preheat the oven to 180C / 350F / 160C fan forced. Line a muffin tin with cupcake papers.
Start by placing the flour, cornflour, baking powder and salt in a bowl and whisk well to distribute everything evenly.
Using a handheld beater or stand mixer with paddle attachment, beat together the butter and sugar until lightened and fluffy (2-3 minutes). Don't skimp on this step and make sure to scrape down the sides of the bowl regularly.
Add the eggs one at a time, beating until combined (scrape down the bowl as needed). Add the vanilla and beat through.
Alternate 1/3 of the flour followed by half the milk, stirring in with a spatula and then repeat until everything is added. Don't overmix at this point.
Fill the cupcake cases to two-thirds full and bake for 20-22 minutes, turning the tray at the halfway mark, until a toothpick comes out with just a crumb or two attached.
FOR THE FILLING AND CUSTARD BUTTERCREAM
Pour 1 1/4 cups of milk into a heavy based saucepan, and add roughly half cup of sugar and the vanilla. Heat on low heat until steaming, stirring regularly. Remove from heat.
In a large bowl, whisk together the remaining 1/4 cup milk, egg yolks and cornflour until smooth and fully combined.
While whisking, very slowly pour the hot milk mixture into the egg mixture in a slow but steady stream. Don’t pour it too quickly or the heat will scramble the eggs.
Once everything is combined, return the mix to the saucepan. Heat over medium heat, stirring with a whisk constantly, until it gets very thick and no longer settles into itself when you move it around. This will happen quite quickly after about 5 minutes so it’s important to keep gently whisking increasing intensity as it gets very thick. Continue cooking while whisking for another minute. You will end up with lumpy custard if you don’t.
Swap to a silicone spatula and pass the custard through a strainer into a clean bowl, then press plastic wrap to the surface and allow to cool to room temperature.
Use an electric butter, or a stand mixer with paddle attachment to whip the butter and remaining 1/4 cup of sugar for about 5 minutes or until it looks very light and airy.
Reserve 1/4 cup of the pastry cream for filling the cupcakes, then add the rest, 1 spoonful at a time, beating for a few seconds to incorporate, before adding the next. Beat well for another minute or so.
Finally mix through the salt.
Use a silicone spatula and just spend a minute stirring and pressing the buttercream against the side of the bowl just to remove any big air bubbles that might make piping difficult.
Cut a 3/4 inch hole in the top of each cupcake with a cupcake corer or sharp knife. Fill with 1 teaspoon of the reserved pastry cream in each, then replace a thin slice of cake on top.
Place the buttercream into a piping bag with open star piping tip and pipe swirls of buttercream on top.
Cake flour is a combination of all-purpose and cornstarch. I use cornflour (cornstarch) often in my bakes so that I don't need to keep cake flour on hand. Feel free to replace both the plain flour and cornflour with cake flour in this recipe.
These cupcakes freeze well, so go ahead and place the ones you don’t need in the freezer for another time. Make sure to wrap them well to keep the air (and hence frost) out. Wrap in one big bundle with a small piece of baking paper on top of each one, in aluminium foil. Then wrap the whole lot well in plastic wrap or in a well sealed, air free, snap-lock bag.
For best results, you should always weigh ingredients like flour and sugar. Kitchen scales are relatively cheap but if you can’t weigh the ingredients, use the spoon and level method (don’t scoop).
Sugar: you can swap the caster sugar in the buttercream for granulated white sugar but don't use powdered or icing sugar.