Put 250 g flour, cream cheese, sour cream and butter in flakes in a bowl. Knead first with the dough hooks of the mixer, then with your hands to a smooth dough. Cover and chill for approx. 45 minutes.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Line two baking trays with baking paper. Roll out the dough thinly on some flour about 1⁄2 cm. Cut out circles (each approx. 5 cm Ø), knead the dough again, roll out, cut out and place a total of approx. 55 circles on the trays.
Whisk the egg yolk and 1-2 cold water. Spread thinly on the dough circles. Prick several times with a wooden skewer, sprinkle with salt. Bake in a hot oven for 18-20 minutes until golden brown. Take out the crackers, pull them off the baking tray together with the paper and let them cool down.