Heat the vinegar with the sugar and water in a saucepan.
Additionally, chop the cucumber and onion and add to the mixture as well as the grain mustard.
Leave to cool.
Cook the sausage in water and then brown it in a frying pan.
Slice the buns in half, spread them with butter and lightly grill.
Add the sausage, a little mustard and the gherkins on top.