For the base, place the sugar and flour in a bowl. Add the butter and rub in until the mixture resembles breadcrumbs.
Add the egg and bring together into a smooth dough. Wrap in cling film and leave to rest in the fridge for 30 minutes.
Preheat the oven to 180°C, gas 4. Grease a rectangular baking dish with butter.
Roll out the dough and use to line the dish. Prick the base with a fork. Bake for 15 minutes. Remove from the oven.
Increase the oven temperature 200 °C, gas 6.
For the topping, separate the eggs. Mix the egg yolks with the quark, sugar, lemon zest and lemon juice. Melt the butter, leave to cool slightly and mix in.
Mix the custard powder with the baking powder and semolina and stir into the quark mixture. In a separate clean bowl, beat the egg whites until stiff and fold in.
Spread the mixture evenly over the base. Arrange the peaches on top. Bake for 40-45 minutes until pale golden and set. If it starts to brown too much, cover with foil.
Leave to cool completely and serve cut into pieces.