Bring milk, 75 ml water, butter and salt to the boil in a saucepan. When the fat is completely melted, add flour all at once. Stir with a wooden spoon until a white layer forms on the bottom of the pot and the dough comes off the bottom of the pot as a lump.
Place in a bowl and immediately stir in 1 egg. Leave to cool for about 10 minutes. Stir 2 eggs bit by bit into the dough.
Pour the dough into a piping bag with a medium perforated spout. Spray the choux pastry in strips onto a baking tray lined with baking paper to form two rectangles (approx. 10 x 30 cm). In a preheated oven (electric cooker: 225 °C/ circulating air: 200 °C/ gas: see
manufacturer) Bake for 15-20 minutes. Remove from the oven and allow to cool.
Soak gelatine in cold water. Cover 1 choux pastry rectangle with a rectangular cake frame (or make a frame from aluminium foil). Mix mascarpone, yoghurt and sugar to a smooth cream.
Squeeze out the gelatine, dissolve and stir in 5 tablespoons of the Mascarpone Cream. Stir the gelatine into the remaining mascarpone cream. Stir in 3/4 of the jam slightly striped and smooth it down on the choux pastry base.
Place the second choux pastry base on top as a lid and chill for about 2 hours.
Remove the choux pastry from the frame and decorate with the remaining jam.