01 -
Melt the butter in a medium saucepan over low heat, then add the milk and grated cheese, stirring until the cheese melts and becomes smooth.
02 -
Add the vinegar, mustard, black pepper and gherkins; stir to combine and remove from heat.
03 -
Allow to cool slightly, stirring occasionally. Preheat the broiler (grill) then place the four pieces of toast on a baking sheet and divide the cheese mixture evenly between them.
04 -
Place under the broiler, until bubbly and hot; place on plates and serve with gherkins/cornichons and salad, if desired.