Cook the frankfurter in a non-stick pan and toast the small baguette cut into halves.
Mix potatoes, beetroots and a spoon of mayonnaise, adding salt and pepper if necessary.
Spread the honey and mustard mayonnaise on the bread; this sauce can be easily found in markets; alternatively, prepare it at home by mixing a spoon of mayonnaise with a teaspoon of mustard seeds and half a teaspoon of honey.
Place the potato and beetroot salad on the base of the sandwich; put the frankfurter on top of it and close the sandwich. Serve the sandwich accompanied by a teaspoon of sauce.