Vanilla swiss meringue buttercream

Method

1. Heat 4cm water in a saucepan over a low-medium heat to a gentle simmer. Put the egg whites and sugar in the bowl of a stand mixer. Rest the bowl over the simmering water and, using a flexible spatula, mix constantly for about 10 minutes or until the sugar has dissolved and the temperature reaches 72°C on the digital probe thermometer. Be sure to keep the water just at a simmer or you risk scrambling the eggs and will have to start again.
2. Once the mixture reaches 72°C, quickly remove from the heat and put the bowl back in your stand mixer, fitted with the whisk attachment. Beat on high until stiff peaks form, then reduce the speed to medium for 6-8 minutes until the outside of the bowl is no longer warm to the touch.
3. Swap the whisk for the paddle and, on a low speed, begin adding the butter in 25g chunks until the mixture is smooth and fluffy (5-10 minutes; see tips). Stir in the vanilla. Set aside 650g buttercream for the limoncello and poppy seed cake.
4. To make the raspberry buttercream, put 300g vanilla buttercream in a mixing bowl. Push the raspberries through a fine sieve with the back of a spoon to make a purée and discard any seeds. Squeeze out as much liquid from the pulp as possible until you have about 100g purée (discard the pulp). Heat the purée in a small pan over a medium heat for 7-10 minutes, stirring continuously, until the mixture thickly coats the back of a spoon and has reduced to about 30-40g. Cool completely, then mix the raspberry purée into the buttercream.
5. To make the passion fruit buttercream, put 850g of the buttercream in a large mixing bowl. Heat the passion fruit purée over a low-medium heat, stirring occasionally, for 10-15 minutes or until very thick. Strain through a fine sieve and cool completely. You should have about 100-115g. Stir about 60-75g purée into the buttercream to taste, adding more as needed. You’ll have buttercream left over; keep this for crumb coating the rosé champagne cake later.