Croque Monsieur sandwich

BÉCHAMEL

2 Tbsps (1oz/28gr) butter

3 Tbsps flour

1 cup milk

1 tsp dijon mustard

½ tsp salt

¼ tsp pepper

ASSEMBLY

8 thin slices of bread (Commons or Sourdough Boule)

8 thin slices of cooked ham (about 6oz)

2+2 oz Gruyère, grated

¼ cup Parmesan, grated

1 tsp herbes de Provence

1. Make the béchamel sauce first by melting the butter, and then whisking in the flour, whisking continuously until the mixture starts to turn golden. Note, this usually makes almost exactly twice as much as I need, but I refrigerate the rest to make more sandwiches, later.
2. Stream in the cream, whisking constantly. Add the dijon, salt and pepper.
3. Whisk until the sauce starts to thicken; it will become quite thick.
4. Meanwhile, with the oven rack at the highest level, pre-heat the oven to 450°F. While the oven is heating up, place the bread on a baking sheet and toast it in the increasing heat, flipping the pieces to lightly toast both sides.
5. To assemble, divide all the ingredients into 4 portions of each item.
6. Spread the béchamel evenly on the bottom piece of toast, going from edge-to-edge and put on the baking sheet.
7. On top of the béchamel place the ham, top with half the grated Gruyère, then place the other piece of toast on top, pressing down firmly. 
8. Mix together the second half of the Gruyère with the Parmesan and herbes de Provence. Top the closed sandwiches with this mixture as the final flourish.
9. Bake in the oven for about 6 to 12 minutes or until the cheese inside is melted; the position of the rack should provide sufficient radiant heat to melt the cheese on top as well. If not, your oven is different than mine, so keep the rack in the middle position and after the 6 minutes, broil the top to melt the cheese. Depending on your oven, 6 minutes may not be enough; the metric you can use is whether or not the cheese on top has started to melt.