1To make the meringues, weigh the egg whites and multiply the weight by 2 to get the amount of sugar to use.
2Preheat oven to 95 degrees Celsius.
3In a small saucepan over low heat cook the sugar and the egg whites, stirring well until the sugar dissolves and reaches a temperature of 37 C. Remove from heat.
4With an electric mixer, beat the egg whites, gradually add the lemongrass powder and keep beating until stiff peaks form.
5Using a pastry bag place small domes of meringue in a baking sheet.
6Bake for 60 minutes, let it cool on a wire rack.
7Prepare the lemon syrup. In a small saucepan, boil the water, sugar and zest of a lemon. Let boil for 10 minutes.
8Preheat oven to 220 C.
9Separate the eggs.
10With the stand up mixer beat the egg whites until foamy, add half of the remaining sugar and continue to beat for about 1 minute, continue adding the remaining sugar and keep beating until stiff peaks form. Add yolks into the egg whites and mix very quickly .
11Pour the sifted flour and fold with a rubber spatula.
12Pour the batter on a baking plate lined with parchment paper.
13Spread the batter with a spatula so its 1cm thick.
14Bake for about 7 to 8 minutes, remove it from the oven.
15Turn the cake over a damp cloth.
16Brush the cake (while it's still hot) with the lemon syrup to soak it, let it cool (5 to 10 minutes)
17Sprinkle the gelatin powder in cold water.
18In a separate bowl, mix eggs, sugar, and lemon juice.
19Bake this mixture at 85 C until thickened.
20Add the gelatin, mixing until well incorporated.
21Cool this mixture to 45°C and then add the butter cut into pieces.
22Mix to get a smooth cream.
23Wrap with plastic film and store in the refrigerator for 30 minutes (not more, or the gelatin will set)
24Spread half of the mascarpone cream on the cake.
25Roll the pie gently but tightly. Cover it and refrigerate for 30 minutes.
26With the electric mixer, beat the remaining mascarpone cream to obtain a smooth and airy texture.
27Take the cake out of the refrigerator and with a spatula ice it with the lemon/mascarpone cream.
28Carefully place the meringues.
29Sprinkle with confectioner's sugar and lime zest.
30Keep cool until serving.
31It can be made up to a day before.