Brush the rolls with egg white and scatter with poppy seeds and bake for a couple of minutes in the oven until warmed through and golden. Cool and split until almost halved.
Slice the potatoes very thinly on a mandolin and place in a bowl of cold water for 10 minutes before rinsing (this removes the starch, which allows for ultimate crispiness). Lay out the potato slices on a tea towel or paper towel and dry as much as you can.
Heat the oil in a large deep pan to 160°c/320°f. Add the chips a large handful at a time and cook for 3-4 minutes until very lightly golden. Drain on a wire rack over a baking sheet. While they are still hot, add a pinch of hot smoked paprika and a pinch of celery salt.
Meanwhile, heat a griddle pan to a high heat and coat the frankfurters in the oil. Add to the pan and cook until brown in colour and cooked through.
Put a sausage into each of the buns, top with a good squeeze of mustard, a dill pickle, a scattering of the onion, some wedges of tomato and sport peppers.
Add a squeeze of tomato ketchup and serve with the crispy potato chips.