Swiss Roll with lime curd and whipped cream

I first learned how to make a swiss roll using these two recipes. Since then I have gotten fairly good at making them.

Here is my latest variation: Swiss Roll with lime curd and whipped cream

Tips before starting: Gather all of the ingredients for both the sponge and the curd, measure them and do what preparation is needed so they are ready to go right into the mixture once you start. If you are using the optional whipped cream, put the mixing bowl, whisk, and leftover storage container in the fridge before you start on the rest of the preparations.

Start the sponge first and work on the curd while the sponge is baking. Save whipping the cream until after the sponge and curd have cooled and are ready for assembly.

Ingredients

For the sponge (cake layer)

• parchment paper
• 4 eggs, three whole eggs plus an egg yolk (reserve the extra white for the curd)
• 160g caster sugar, plus extra for rolling
• 160g all purpose flour
• 1 ½ tsp baking powder
• ½ tsp salt 

For the lime curd

• 55g unsalted butter
• 55g caster sugar
• 2 limes, zest and juice
• 1 egg + 1 egg white beaten

Optional: whipped cream

Instructions 

For the sponge:

• preheat the oven to 200C/400F/Gas 6
• line a 10½x16in (26x40cm) baking tray with baking parchment. If possible use a tray with raised edges. If you don't have one, use a slightly larger cookie sheet so the batter won't expand over the edges.
• place a large heatproof bowl over a pan of simmering water. 
• add the eggs and sugar to the bowl and whisk until lukewarm (~100F/38C). 
• remove bowl and whisk until the mixture is very thick and leaves trails when the whisk is removed. This can take 10-20 minutes by hand.
• fold in the sifted flour using a spoon with a slim profile (metal or silicone, not thick wood)
• the batter will be about the consistency of crepe batter but with more air in it
• spread the mixture thinly onto the prepared baking tray. I find pouring it from the bowl into the shape I want works best-- it is difficult to spread once poured. 
• place on the middle shelf in the oven and bake for 8-10 minutes, or until it springs back when touched. Don't overtake or it will be difficult to roll.
• lay a large piece of baking parchment over a tea towel and  dust the parchment with sugar. 

For the curd (while the sponge is baking)

• set a large heatproof bowl over a pan of simmering water
• put the butter, sugar, lemon zest and juice into the bowl
• stir occasionally until the sugar is dissolved 
• once the sugar is dissolved, add the beaten eggs
• stir occasionally, until the mixture shows signs of thickening
• stir more regularly until the entire mixture has thickened
• transfer to a clean bowl to cool (this speeds the cooling process)

Final steps for sponge

• once the sponge is baked, tip it out onto the dusted baking parchment and carefully peel off the baking parchment it was cooked on.
• roll the sponge while it is still hot. Start from the short end and roll the parchment up with the roll so it will unroll nicely later. Use the towel to help protect your fingers and to hold the final roll together while it cools. Don't roll the towel up inside the roll. 
• set the sponge aside to cool with the curd-- approximately 30 minutes

Assembly

• if using whipped cream, whip it up now
• un-roll the sponge and spread the lime curd thinly and evenly over it
• spread a slightly thicker layer of whipped cream over the curd
• re-roll the sponge, note that some of the whipping cream will squeeze out as you roll
• trim the ends of the roll to create a neat finish and give yourself a little treat
• dust with icing sugar or pipe some of the extra cream on as a decoration or leave plain

Store in the fridge in an air tight container or wrapped in clingfilm when not serving. There will be left over cream and lime curd. Store both in airtight containers in the fridge as well.

Previous variation: Swiss roll with cinnamon, coffee, and hazelnut