Method
For the lemon curd
For this you will need a heatproof bowl that can be sat over a pan of just simmering water. The bottom of the bowl must not be able to touch the water.
While the water in the pan is heating up, prepare the ingredients. Zest one of the lemons and put this aside for using in the sponge.
Zest 1½ of the remaining 2 lemons and place in the bowl.
Juice all 3 lemons and add this to the bowl (the 3 lemons should produce about 9 tablespoons of juice).
Add the eggs and sugar.
Whisk all the ingredients together and then place the bowl over the pan of simmering water.
Now whisk in the butter, a little at a time. Let the butter melt between each addition and whisk until all the butter is blended in.
Then stir the curd occasionally to keep the mixture smooth and cook until the curd has thickened, about 15 minutes.
Remove the bowl from the pan and let the mixture cool.
Cover the curd with clingfilm/plastic wrap to prevent it forming a skin and refrigerate so it has a chance to become well chilled.
For the sponge
Preheat the oven to 200°C (400°F) (gas 6).
Put all the ingredients except the icing sugar/powdered sugar in a large bowl and whisk for 1 minute. Use either an electric hand mixer or a free-standing food mixer.
Heat a little water and add 1 tablespoon to the mixture and whisk briefly, just enough to mix in.
Now spoon the mixture into the prepared baking tin and smooth it out to an even layer.
Bake for 8 to 10 minutes but do not open the oven door before 8 minutes has elapsed or the sponge could sink. The sponge is cooked when if feels springy in the centre if lightly touched with the forefinger.
Remove the cake from the oven and leave it for 5 minutes to cool in the tin.
Meanwhile, cut a piece of baking parchment 40 cm (16 in) long and lay it flat.
Heavily dust all over with icing sugar/powdered sugar.
Turn the sponge out onto the sugared paper and carefully remove the lining paper. Now dampen a thin tea towel and lay over the sponge and leave for 3 minutes. This will make it easier to roll the sponge but it needs to still feel slightly warm.
To roll up the sponge, lift the paper from one of the shorter sides and fold it over the edge of the sponge. Carefully roll up the sponge and the paper together as tightly as possible. Gently lift onto a wire rack to cool completely.
For the cream filling
Whisk together the mascarpone, fromage frais, and sugar until soft and creamy.
To assemble
Unroll the sponge and evenly spread all-over with two-thirds of the lemon curd and two-thirds of the cream filling.
Now gently roll up the sponge again but this time more loosely and then lift carefully onto a serving plate.
For the icing and decoration
Using a zester, remove the zest from the lemon to get long, curly strands and put on a small plate. Sprinkle over about half a tablespoon of lemon juice and stir to coat the zest strands.
Now to make the icing, sift the icing sugar/powdered sugar into a small bowl and stir in about one tablespoon of lemon juice, enough to make a thin glaze. Using a spoon, and starting at one end, quickly drizzle the glaze across the roulade back and forth, working down the roulade to the other end.
Tip the zest onto a piece of kitchen paper to absorb any excess lemon juice and then scatter the zest over the top of the roulade.
Stir the remaining lemon curd and cream filling together and spoon into a small serving bowl.
The roulade is then ready to be sliced and served with a spoonful of the lemon cream.
