For the shortcrust pastry, pour 400 g flour on the work surface. Press a depression in the middle. Add 200 g sugar, baking powder, 1 packet of vanilla sugar and 3 eggs. Spread 150 g butter in small pieces on the edge of the flour.
Knead everything into a smooth dough with your hands as quickly as possible. Halve the dough.
Squeeze lemon for the filling. Melt 4 tablespoons of butter in a pan. Fry the crumbs and pine nuts until golden brown. Remove from heat and let cool off. Peel, quarter and core apples. Finely slice the apple quarters.
Mix immediately with 4 tablespoons of lemon juice, 4 tablespoons of sugar, 1 strong pinch of cinnamon, 1 packet of vanilla sugar and the breadcrumbs-pine nut mix.
Line a baking tray with baking paper. Preheat the oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Roll out one half of the dough rectangularly (approx. 30 x 37 cm) on the floured work surface.
Place half of the apple mixture as strips lengthwise on the middle of the dough, leaving a margin of about 2 cm on the short sides. Whip one long side first, then the other over the filling.
Turn in short sides. Prepare second strudel in the same way.
Place both strudels on the baking tray. Whisk 1 egg and brush the strudel with it. Bake in a hot oven for about 40 minutes. Take them out and let them cool down a little on a cake rack. Serve lukewarm with half-stiff whipped cream.