Beat the softened butter and 100 g sugar with the whisk of the hand mixer until foamy. Separate the eggs. Stir the egg yolks into the fat-sugar mixture. Add lemon juice and zest. Stir in flour and baking powder.
Beat the egg white until stiff and stir into the dough in portions. Pour the dough into four small, well greased baking tins and bake in a preheated oven (electric range: 175 °C/ gas: level 2) for 20-25 minutes. In the meantime, stir 50 ml milk and starch until smooth. Bring the remaining milk, cream, remaining sugar and vanilla sugar to the boil in a small pot. Lightly beat the egg yolks with a fork. Add the whisked starch while stirring, and bring to the boil briefly. Remove from the heat and stir in the beaten egg yolk. Add orange juice. Take the tartlets out of the oven, dust with icing sugar and add some sauce.
Add the whisked starch while stirring, and bring to the boil briefly. Remove from the heat and stir in the beaten egg yolk. Add orange juice. Take the tartlets out of the oven, dust with icing sugar and add some sauce. Serve immediately, decorated as desired with orange and lemon balm. Add the rest of the sauce