Remove the pistachios from their shells and chop them coarsely. Clean, wash and coarsely grate the zucchini, except for the soft inside. Wash the lime hot, dry it and grate the skin thinly. Preheat oven (electric cooker: 180 °C/circulating air: 160 °C/gas: see manufacturer). Grease a box form (30 cm long; approx. 2 l capacity) and dust with flour.
Cream 200 g butter, sugar, vanilla sugar, honey and 1 pinch of salt with the whisk of the mixer. Stir in the eggs one after the other. Mix 375 g flour and baking powder, alternating with 100 g yoghurt. 2⁄3 Briefly stir in the pistachios, lime zest and zucchini. Fill the dough into the form, smooth it down and bake for about 45 minutes. Cover the cake if necessary about 10 minutes before the end of the baking time. Place on a cake rack and leave to rest in the tin for approx. 30 minutes. Turn the cake out of the tin and let it cool down.
For the frosting, stir 30 g yoghurt and icing sugar until smooth. Spread the icing on the cake. Sprinkle with the rest of the pistachios and leave to dry a little.