Method

• 1.
  To make the sponge, preheat oven to 160°C conventional. Lightly grease 6 x 1-cup (250ml) capacity sphere moulds (see recipe notes) and dust with flour, tapping to remove excess flour.
• 2.
  In a stand mixer fitted with the whisk attachment, whisk the eggs, extra yolk, sugar and lemon zest for 4-5 minutes, until pale, thick and soft peaks form. Sift over the flour and cornflour, then gently fold to combine (do not overmix). Divide between prepared moulds and bake for 20-25 minutes, until lightly golden and springy. Stand for 2-3 minutes, then turn out onto a wire rack to cool completely.
• 3.
  For the limoncello syrup, combine all ingredients in a small saucepan with 35ml water and bring just to the boil. Set aside to cool completely.
• 4.
  For the lemon cream, place the lemon zest and juice and the butter in a medium saucepan over medium heat until the butter melts. Whisk egg yolks and sugar in a large bowl until pale. Gradually whisk in the warm lemon mixture until combined. Return to pan and cook over low heat, stirring constantly with a wooden spoon, for 10 minutes, or until thickened and mixture coats the back of spoon. Strain into a bowl, cover with plastic wrap, ensuring that plastic wrap is touching the surface, and poke a few holes in wrap with a skewer. Set aside to cool.
• 5.
  For the custard cream, combine the milk, cream, lemon zest and vanilla in a medium saucepan. Cook, stirring occasionally, over medium heat until just simmering. Whisk egg yolks, sugar and cornflour in a large bowl until pale. Gradually whisk in the hot milk mixture until combined, then return to pan. Cook over medium heat, stirring constantly, for 5-6 minutes, until mixture starts to simmer and thicken. Whisk until smooth, then strain into a bowl. Cover with plastic wrap, ensuring plastic wrap is touching the surface, and poke a few holes in wrap with a skewer. Set aside to cool.
• 6.
  For the lemon glaze, whisk the thickened cream until soft peaks, then fold through 150g of the cooled lemon cream until combined. Add milk to loosen slightly – it should be soft and pourable, not runny. Set aside at room temperature.
• 7.
  To assemble, line a baking tray that fits in your freezer with baking paper. Using a small knife, make a hole in the base of each sponge. Combine the custard cream and remaining lemon cream in a large bowl, then spoon into a piping bag fitted with a 1cm plain nozzle. Fill each sponge generously from the base, turning the nozzle to fill entire sponge (the sponge will feel heavier and look fuller). Place sponges, dome-side up, on prepared tray.
• 8.
  Using a toothpick or skewer, gently prick the sponges all over. Brush generously with the limoncello syrup, allowing it to soak in fully. Freeze sponges for 1 hour to firm up.
• 9.
  Place sponges on a wire rack placed over a baking tray. Drizzle the glaze over each sponge, letting excess drip into the tray. Chill for at least 1 hour to set, then serve sprinkled with extra lemon zest.