Preheat the oven to 175C (fan) and line two large trays with non-stick baking paper. If you only have one tray, that's fine as it's best to bake these one tray at a time anyway (you'll just have to pipe the sponge fingers twice rather than all in one go)

In a large bowl. whisk the egg whites with an electric hand whisk until foamy and forming soft peaks (about 2 minutes of whisking).

Add 50g of the sugar to the egg whites and whisk again, until the mixture starts to look glossy and forms stiff peaks (about 5 minutes).

In a second bowl, whisk the egg yolks with the remaining 30g caster sugar and the vanilla bean paste. Whisk for about 3 minutes, until pale and fluffy.

Tip the egg yolk mixture into the bowl with the egg whites. Fold the two egg mixtures together, slowly and carefully so as not to knock the air out. I use a spatula for this, scooping the mixture from underneath and at the sides, then mixing with a slow cutting action.

Now sift about a third of the flour over the eggs, then fold it a couple of times. Then another third of flour and fold a couple of times. Finally sift the remaining flour, baking powder and salt into the bowl. Then fold the mixture until nicely combined and smooth. Doing it in this gradual way, should avoid any flour lumps forming and mean less mixing, so you keep as much air as possible in the mixture.

Place a piping bag fitted with a round nozzle (I use Wilton 1A) in a tall empty glass. This will help the bag to stand up while you fill it. Scrape all the batter into the piping bag.

Pipe ladyfingers about 10cm long, 2cm wide onto the trays, leaving some space between them as they will grow and spread a little during baking.

Dust the ladyfingers really liberally with icing sugar - ensuring they each get a good coating. During baking this will turn into a lovely shiny crust on the outside of the biscuits, giving them a nice crunch while the inside stays softer.

Bake them (on the lower shelf of the oven), one tray at a time, for 12-14 minutes until lightly browned. Once baked, allow to cool for a minute or two on the tray, before carefully transferring them to a wire rack (they may stick a little bit to the paper, use a metal spatula or knife to gently ease them off). Once cooled, either use (or eat!) immediately or store in an airtight container until needed. They will keep for a couple of days, when stored properly.