Step 1

Preheat the oven to 200C/400F/Gas Grease and line a 33cm x 23cm/13in x 9in Swiss roll tin with buttered baking parchment.

Step 2

Put the eggs, 115g/4oz sugar and the lemon zest in a heatproof bowl.Place over a pan of gently simmering water. Whisk with an electric whisk until the mixture is pale, creamy and thick enough to leave a trail when the whisk is lifted. Carefully remove the bowl from the heat and continue whisking for a further five minutes.

Step 3

Sift in half the flour and, using a large metal spoon, lightly fold it into the egg mixture. Sift in the remaining flour and fold into the mixture - it’s important to use gentle movements to retain as much air as possible in the batter.

Step 4

Pour the mixture slowly into the prepared tin and gently spread with a spatula so the base of the tin is evenly covered.

Step 5

Bake for 10–12 minutes until well-risen, pale golden-brown and firm to the touch.

Step 6

Place a damp tea towel on the work surface and cover with a sheet of baking parchment. Dredge with the four tablespoons of sugar – this will help stop the outside of the sponge sticking. Working quickly, turn the cake out onto the sugared paper and carefully remove the lining paper.

Step 7

Using a sharp knife, cut off the crusty edges from the two long sides. Roll the Swiss roll from one of the short ends, starting with a tight turn to make a good round shape and keeping the sugared paper inside the roll. Set on a wire rack and leave to cool.

Step 8

To make the icing, put the icing sugar and butter in a bowl and beat until smooth and creamy. Add the lemon juice and beat again.

Step 9

When the cake is cold, gently unroll but do not flatten it or it could crack. Spread the cake with then lemon butter icing, leaving a 1cm/½in border. Spoon the lemon curd evenly over the icing. Slowly roll the cake up again, enclosing the filling, and place on a plate. Sprinkle with extra sugar if you like.