8 slices firm-textured white bread, crusts trimmed
Put the Gorgonzola in a small bowl and break it into small pieces with a fork. Add the olive oil and mash until creamy.
Put the mâche in a bowl. Add the creamed Gorgonzola, a little at a time, turning the leaves gently with a fork until evenly coated.
Mound one-fourth of the mâche and Gorgonzola filling in the center of each of 4 slices of bread; top with the other slices. Position a sharp knife diagonally across the slice of bread; hold the bread down with your other hand so as not to flatten the filling and quickly slice the sandwich to produce two tramezzini.