For the decorative roses, knead 600 g fondant more smoothly. Shape into rose petals.
Grease a springform pan (26 cm Ø; with approx. 7 cm high rim) and dust with flour. Preheat the oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Cream 300 g butter, sugar, vanilla sugar and 1 pinch of salt with the whisks of the mixer.
Add lemon zest and 4 tablespoons of lemon juice. Stir in 6 eggs individually. Mix 375 g flour and baking powder and stir in. Put the dough into the form, smooth it down. Bake in a hot oven for about 1 hour, 10-15 minutes before the end of the baking time, cover with aluminium foil if necessary.
Let it cool down.
Remove the base from the mould and cut through horizontally twice. Spread half of the Lemon Curd on the lower bottom. Place the second base on top and spread the rest of the curd on top. Place the upper base on top.
For the icing, sieve 400 g icing sugar into a bowl. Add 2 egg whites and whisk with the whisks of the mixer for about 5 minutes until thick and creamy. Gradually add approx. 4 tbsp. lemon juice until the mixture is thick but still spreadable.
Spread the cake thinly with approx. 1⁄4 of the icing to bind crumbs. Leave to dry for approx. 30 minutes, covering the rest of the glaze well with cling film. Coat the cake with the remaining icing and place on a cake plate.
Knead 200 g fondant. Roll out to a rectangle (approx. 10 x 60 cm) on a work surface dusted with icing sugar. Divide the rectangle into three and roll out the strips very thinly, approx. 75 cm long.
Cut strips straight so that they are about 2 cm wide. Brush the bottom edge of the strips with a little water. Place them on the top edge of the cake once all around and press them down carefully. Process the remaining strips in the same way and always stick them under the top strip.
Decorate the cake with the fondant roses.