Preheat the oven to 200°C.
Open the pack of pastry and unroll it on its packaging.
Cut the each of the frankfurters into three equal chunks. Use one of them to measure the width of pastry.
If you want the pastry to overlap the sausage then cut the pastry into wider strips than the length of your frankfurter third.
If you want the sausage to protrude at both ends, cut the width of the pastry about 1 cm less than the length of your sausage piece.
Now place one sausage portion on the top of the strip and roll until the pastry covers it and slightly overlaps creating a seal. Cut the pastry here.
You now have a rectangular shape. Use this as your template and cut up the pastry.
Then quickly brush each pastry piece with ketchup &/or mustard and roll up the frankfurter portions in the pastry.
With the seal downwards place them onto a lined baking tray.
If you have time, rest in fridge for 10 minutes.
Brush the top with egg (optional) and bake for 12-15 minutes until golden brown.
Serve warm or at room temperature.