Heat oven to 180C/160C fan/gas 4. Grease and line bases of 3 x 20cm sandwich tins. Beat the butter, sugar, flour, eggs, almonds, yogurt, all the zest and half the lemon juice. Divide between the tins and bake for 20-25 mins until a skewer poked in comes out clean (you may want to change the shelves around after 20 mins to ensure the cakes cook evenly). Mix the juice of the second lemon with 1 tbsp sugar, poke the cakes a few times with a skewer and drizzle over. Cool in the tins on wire racks.
Sandwich the 3 sponges together with 8 tbsp of the lemon curd. Brush the rest over the top and sides of the cake. Break off 50g marzipan, then roll out the rest on an icing sugar-dusted surface until large enough to cover the cake. Cover the cake with the marzipan and transfer it to an upturned bowl or saucer on a tray, so the edges of the cake overhang the bowl, but it is stable.
Mix enough water into the fondant icing sugar to make a thick icing. Set aside a few tbsp, then mix some yellow food colouring into the rest. Spoon bit by bit over the cake, letting it dribble down the sides until the entire cake is covered (and excess has dripped off).
Knead pink colouring into half the marzipan and green into the other half. Roll out the green and cut out leaves. Use a cocktail stick to draw veins on. Press bits of the pink into long, flat sausages and roll up to look like roses. Put the reserved white icing into a food or piping bag. Snip the end and pipe fine squiggles over the cake. Add roses and leaves once the icing is almost set.