Preheat oven (electric cooker: 180 °C/circulating air: 160 °C/gas: see manufacturer). Line the bottoms of the springform pans with baking paper. Wash 6 limes hot, dab dry and finely grate the skin. Squeeze the juice (later for the cream).
For the dough, whisk 250 g soft butter, half lime zest, 225 g sugar and 1 pinch of salt with the whisks of the mixer for about 4 minutes until creamy. Stir in 5 eggs one after the other. Sift 225 g flour and 1⁄2 packet of baking powder. Mix with 80 g almonds and fold into the butter-sugar-cream with a dough scraper. Fill the dough into the moulds at the same height, smooth it down. Bake in a hot oven for 30-40 minutes (remove the smallest cake after about 25 minutes; stick test!).
Remove the larger cakes as well, let them cool down and remove them from the moulds. Wash the springforms and line them again with baking paper. Mix the second half of the dough as described above, bake and let the cakes cool down.
Prepare a citrus jelly for the cream. Wash 2 limes, dab dry and finely grate the peel. Squeeze the limes. Fill up to a total of 400 g with the lime juice from the dough and lemon juice set aside. Boil up with jam sugar. Remove from the heat, add the lime zest and let it cool down to room temperature.
Whip 1 kg soft butter for approx. 8 minutes until light creamy (best in a food processor). Stir in several portions of citrus jelly.
Straighten all cakes and cut them in half horizontally. Put each of the 4 large, medium and small cake bases together to make cakes. For this purpose, first put approx. 1 tsp. citrus cream on each cake board so that the cakes do not slip later. Place the matching cake base on top. Spread the cream about 1 cm thick. Place the cake base in the same size on top. Repeat the process twice more per cake. Chill the cakes for about 30 minutes. Then round
For dressing the large cake approx. 2⁄3 Knead fondant briefly. Roll out on a work surface dusted with icing sugar to a thickness of approx. 4 mm (at least 40 cm Ø). Place over the cake and smooth the surface with the cake smoother. At the edge of the fondant, first hold the fondant slightly away from the cake with one hand, then spread it on the edge of the cake with the other hand (first remove some of the fondant from the cake, then spread it down the edge). Smooth all around with the smoothing tool. Cut off any excess fondant, knead again. Clothe smaller cakes in the same way. Cover with foil and chill.
Colour the rest of the fondant as desired with food colouring and shape into flowers or cacti. Leave to dry.
Mix the icing according to the package instructions. Remove approx. 2 tablespoons of icing per colour and colour in. Pour into piping bag. For a secure hold and support, place 3-4 straws in the middle of the large cake (straws in the bottom and middle cake support the tower). Spread some white icing on top. Place the middle cake (with cardboard!) on top. Also put straws into it and spread some icing on it. Place the smallest cake on top. Cut a small corner from the piping bags. Decorate the cake with coloured icing (dots, zigzag lines). Place fondant rosettes or cactuses with white icing on the cake, let dry for about 30 minutes.