For the pudding, stir the pudding powder, 75 g sugar and 100 ml milk until smooth. Bring 400 ml milk to the boil, stir in the pudding powder, bring to the boil and simmer for about 1 minute. Pour pudding into a bowl, cover directly on the surface with foil. Let it cool down.
For the dough, mix 250 g butter, 250 g sugar, lemon zest and 1 pinch of salt until creamy. Stir in the eggs one by one. Mix flour and baking powder, stir in. Spread the dough on a baking tray lined with baking paper (approx. 35 x 40 cm). Bake in a preheated oven (electric cooker: 180 °C/circulating air: 160 °C/gas: see manufacturer) for approx. 25 minutes. Let them cool down.
For the buttercream, whisk 300 g butter with the whisks of the mixer for approx. 10 minutes until creamy. Stir the pudding until smooth and stir in by the spoonful.
Cut the cake plate in half crosswise. Stir jelly until smooth and spread on 1 cake plate. Ca. 2⁄3 Spread the cream on the jelly. Place 2nd plate on top and spread with the rest of the cream. Sprinkle with brittle and press down lightly. Chill the cake for about 1 hour. Cut into small cubes.