Pour sugar, eggs, and lemon juice into a saucepan and whisk it together over low heat for 5 minutes. It must not come to a boil.
Add the lemon zest and butter and continue whisking. It will start to thicken now.
Then strain the mixture into a jar and refrigerate it for a couple of hours.
Preheat the oven to 180 degrees Celsius (356 degrees Fahrenheit) (conventional oven).
Whisk eggs and sugar until airy and white.
Sift flour, baking powder, and vanilla sugar into the egg mixture and add the juice and zest from the two lemons, then whisk it together.
Divide the batter into two springforms lined with parchment paper at the bottom and greased with butter on the sides. My pans are 24 centimeters in diameter.
Bake the cake layers, one at a time, in the middle of the oven for 30 minutes, then let them cool.
Put egg whites and powdered sugar in a bowl.
Whisk together until the meringue is stiff and glossy.
Bring water and sugar to a boil, so the sugar dissolves.
Cut thin slices of lemon and put them into the sugar syrup and let them cook for about 5 minutes.
Lay the cooked lemon slices on a piece of parchment paper and let them cool before placing them on the cake.
Place one cake layer on a cake stand and spread a good layer of lemon curd on the bottom.
Cut the second cake layer in half horizontally to get two thinner layers.
Place one of the thin layers on top of the spread bottom layer.
Spread another layer of lemon curd and place the last cake layer on top.
Now frost the cake with meringue and decorate the cake with extra meringue roses and "blobs" to taste.
Torch the meringue with a kitchen torch right before serving and garnish with candied lemon slices.