Oh my goodness this is as rich and decadent as it looks and so, so lovely on a cold winter’s night! Borrowed from Melissa Clark’s book ‘Dinner in French’, I roughly doubled her original recipe to make a 9 x 13 lasagna pan sized casserole, so you can do what works for you…but know that if there’s any leftover, they reheat into crispy perfection in a skillet – enjoy!
Sauce – this is a good amount for a 9 x 13 pan
1/2 c. EACH butter AND flour
3+ c. whole milk, warm – thick sauce is perfect, but it needs to be pourable so add more as required
~4 c. grated Gruyère – this is going in the sauce and in the sandwiches
1 t. herbes de Provence (or dried thyme)
pinch of kosher salt AND nutmeg
The Rest – adjust the amounts to what you need
12 slices sturdy sandwich bread
Dijon mustard – preferably whole grain
500 g thinly sliced ham – I used shaved deli ham and really loaded up my sandwiches
grated Parmesan for sprinkling on at the end of baking to brown the top (I forgot this)
To make the sauce – melt the butter in a large skillet and whisk in the flour over medium heat until the mix is golden and bubbling. Slowly whisk in 3 cups of milk and continue to whisk until smooth and the mix begins to simmer. Remove the skillet from the heat and stir in 2 to 3 cups of the Gruyère and the spices and then taste for seasonings and adjust as needed. Remember that this is being poured over sandwiches and baked, so perfection is necessary.
Preheat the oven to 375 and butter a deep 9 x 13 lasagna-type casserole dish. Lay out your sandwich bread and begin assembling with a healthy dollop of mustard spread on one slice, a layering of ham, a sprinkling of Gruyère and then a firm squish down with the second slice of bread before you cut each sandwich in half.
Layer the sandwich halves in the prepared casserole dish, cut side up and then scrape/pour the sauce over all. Bake for 45 minutes to an hour until brown and bubbling, and (if you remember to) near the end of cooking, sprinkle on some Parmesan and broil for a couple of minutes to crisp up the top. We enjoyed this with a big green salad, and it really is as heavenly as it sounds.