Start by toasting two pieces of pain de mie bread then shred 3-4 ounces of gruyere cheese.
Spread a couple of tablespoons worth of the bechamel on the bottom slice of the bread, just enough to cover it.
Top that with a generous amount of gruyere cheese along with 6 slices of ham, topping with another generous amount of gruyere, spreading the bechamel on the top slice of bread before placing on top.
Before toasting, spread another layer of bechamel on top of the sandwich and another layer of gruyere cheese.
Place into a 375°F oven until thoroughly brown and bubbly.