Preheat oven to 400’ F. To make the béchamel sauce, melt butter in a medium saucepan over medium heat until foamy. Add in flour and cook, stirring constantly for about 3 minutes, until foamy and raw flour flavor is gone. Whisk in milk and add a couple of dill sprigs. Continue whisking until the sauce is thick (3-5 minutes). Remove from the heat and whisk in 2 tbsp of mustard and nutmeg. Season with salt.

Line a ¼ sheet pan with parchment paper and lay 2 slices of bread on it. Butter the tops of both slices of bread with remaining butter. On one of the slices, layer your ham, a nice slathering of béchamel (end to end coverage) and gruyere. On the other slice, spread the remaining mustard.

Close the sandwich (butter/mustard side down) and slather the top with more béchamel. Grate some parmesan on top of that, season with pepper and garnish with dill sprigs. Note: Make sure to spread your béchamel on the bread end to end and in a fairly thin layer.

Bake in the over for about 15 minutes or until the top is nicely browned. Cut in half and enjoy it while it’s hot!