Mix flour, sugar and salt.
Add cold butter pieces and mix in a food processor until the lumps have the size of peas. (Or crumble with hands but be careful, the dough should not get warm.)
Add ice water and knead until it forms to a dough.
Press dough to a disk, wrapp in cling film and leave to rest in refrigerator for 1 hour.
Half and pit the peaches, cut into slices.
Mix in a bowl the sliced peaches, sugar and corn starch.
Roll out the dough on a floured surface about ½ cm thick.
Transfer the dough sheet on a baking tray with baking paper.
Spread the peaches on the dough sheet, leaving 3 cm around the edge.
Fold in the edges. Brush the edge with milk and sprinkle with brown sugar.
Bake in preheated oven at 200° C for about 50 minutes.