Preheat oven (electric cooker: 180 °C/circulating air: 160 °C/gas: see manufacturer). Line two trays with baking paper. Unroll dough, spread butter on top. Stir the jam until smooth and spread on top. Roll up the dough from the long side.
Cut the roll of dough alternately diagonally into about 9 pieces, so that one side of the pieces is 3 cm long and the other 5 cm long. Place them on the trays with the wide side down. Press in the middle. Whisk the egg and milk and spread on the Franz rolls. Sprinkle with sugar crystals. Bake in a hot oven for about 15 minutes one after the other until golden brown.