Wash and clean the gooseberries and drain well. Put 500 g gooseberries, lemon juice and jam sugar in a wide pot, bring to the boil and let it boil fizzily for about 3 minutes. Remove from the heat, stir in 200 g gooseberries, place in a bowl and allow to cool for about 2 hours.
In the meantime, mix flour, butter in pieces, 1 pinch of salt, 70 g sugar, egg yolk and 2-3 tablespoons of cold water, first with the dough hooks of the hand mixer, then with your hands to a smooth dough. Roll out the short pastry on a floured work surface until round (approx. 30 cm Ø).
Using a dough roller, place the dough in a greased, flour-sprinkled tart mould (26 cm Ø; with lift-off base), press the edge of the dough lightly, cut off any excess dough. Chill the short pastry for about 30 minutes.
Spread the cooled compote on the bottom, bake in the preheated oven first on the lower shelf (electric oven: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for about 20 minutes. Then bake the tart on the middle shelf at the same temperature for about 20 minutes.
In the meantime, beat the egg whites and 1 pinch of salt with the whisk of the hand mixer until stiff, while pouring in 200 g of sugar. About 10 minutes before the end of the baking time, spread the beaten egg white loosely on the tart and bake until done.
Remove and let it cool down on a cake rack.