Lemon Swiss Roll

• 4 large eggs
  
• 115g caster sugar, plus 2 tablespoons extra
• 1 lemon, rind and juice
  
• 115g plain flour
  
• 200g icing sugar
  
• 150g unsalted butter, very soft
  
• 250g lemon curd, see recipe

For the lemon curd:

• 3 large lemons, rind and juice
• 4 large egg yolks
  
• 100g caster sugar
  
• 100g unsalted butter

1. Preheat the oven 190oC/gas mark 5. Grease and line a swiss roll tin 25cm x 38cm with baking parchment.
2. Put the eggs, 115g caster sugar and grated lemon rind into a heatproof bowl. Whisk the mixture over a saucepan of simmering water until it is pale, fluffy and thickened. Then remove it from the heat and continue to whisk until the mixture is cool.
3. Sieve the flour. Add in one-third of the flour at a time and very gently fold into the egg mixture. Pour the mixture into the swiss roll tin and bake immediately for about 10-12 minutes. It should feel firm to the touch when it is cooked.
4. On the work surface, place a clean tea towel with a piece of baking parchment on top. Sprinkle with 2 tablespoons of sugar. Once the cake is cooked, quickly turn the cake out onto the parchment paper. Remove the swiss roll tin and peel off the baking parchment paper from the bottom. Score the cake with a knife about 2.5cm along the sponge. This helps when rolling it. Roll the sponge while the cake is still hot away from you. Roll up tightly, then leave on a wire rack to cool.
5. To make the curd, grate the rind and juice the lemons. Pour into a heatproof bowl and whisk in the egg yolks and sugar. Place this over a saucepan of simmering water. Make sure the bowl fits snugly into the saucepan and no steam can escape. Continue whisking until the mixture becomes very thick. Remove from the heat, then cut the butter into cubes and stir it into the curd. Allow to cool completely.
6. Sieve the icing sugar into a bowl. Add the butter and whip until very light and fluffy. Mix in the lemon juice and 50g of the lemon curd.
7. Once the swiss roll sponge is cold, carefully unroll. Don’t try to flatten it or it may break. Spread the lemon buttercream filling over the sponge, then the remaining lemon curd. Gently roll up the swiss roll and trim the edges.

To make a chocolate swiss roll, omit the lemon and 30g of plain flour and replace it with 30g of cocoa powder. Spoon chocolate spread instead of lemon curd in the swiss roll. Use 150g icing sugar and 50g cocoa powder for the buttercream filling.