Begin by hulling the strawberries, and cutting any larger ones in half or into quarters. Add the sugar, lemon juice, and liqueur if using. Leave to steep for a couple of hours.

In a large bowl, whisk the egg yolks, vanilla sugar, and caster sugar together with an electric whisk until pale and creamy. Add the pistachio butter and whisk again. Mix in the mascarpone until everything is well combined.

In a separate bowl, whip the double cream until soft peaks form when the whisk is removed. Using a metal spoon, gently fold the whipped cream into the pistachio, mascarpone, egg, and sugar mixture.

In another very clean bowl, whisk the egg whites until soft peaks form. Fold them lightly into the pistachio cream mixture, being careful not to knock out too much air.

Strain the liquid from the strawberries into a shallow bowl and set aside.

Now, briefly dip each sponge finger into the strawberry liquid — don’t leave them to soak or they’ll become too soggy — then immediately lay them in your serving dish. Add half of the strawberries on top of the sponge fingers, followed by half of the pistachio cream. Repeat the process: sponge fingers, the remaining strawberries, then spoon over the final layer of pistachio mascarpone cream.

Cover and chill in the fridge for 4–5 hours, or overnight if possible.

When you’re ready to serve, scatter over some chopped pistachios and decorate with edible flowers, if desired.