For the cheese sauce:
Start by preparing the sauce: cut the Emmental cheese into small pieces. Melt the butter over a gentle heat in a small pot, add hot milk, flour and a pinch of salt. Stir with a whisk to avoid lumps and keep stirring until the cream thickens. Remove from the fire and add Emmental, stirring vigorously to melt it.
Now that the cream is ready, deal with the other ingredients: cut the bread into two horizontally, creating a sort of bag, and grill it in the oven to the highest temperature.
Grill the frankfurter for 10 minutes on a high heat, turning it to cook it evenly.
Use your hand to mince the tortilla chips. Spread the cheese sauce on the lower half of the bread, add the frankfurter, complete with ketchup, cheese sauce and minced tortila chips. Serve when hot.