Start gathering your ingredients. Melt the butter in a saucepan over medium heat. Once melted, add the flour, whisking continuously for around 2 minutes until the mixture turns a light golden color. Gradually add the warm milk, whisking until smooth. Cook it until it thickens, then stir in the nutmeg, sea salt, and freshly cracked black pepper.

Remove the sauce from the heat. Now, stir in the Gruyere and Parmesan cheese until melted. Add the minced thyme and smoked paprika. Taste the sauce and adjust seasoning if necessary.

Toast slices of the rustic artisan bread until golden brown. A toaster or grill works perfectly for this. You want that lovely crispiness that can hold up to the filling.

Spread a generous amount of Dijon mustard on one side of each slice of bread. Layer one slice with a hefty portion of the béchamel sauce followed by the smoked ham and spinach. Top it with another layer of Gruyere cheese. Finish with the other slice of bread smeared with mustard on the inside.

Brush the outside of the sandwich with extra virgin olive oil. Heat your skillet over medium heat. Place the sandwich in the skillet, pressing down gently. Cook until it’s golden brown on one side, then flip and repeat on the other side. Both sides should have a lovely crunch.

Once your sandwich is golden brown and the cheese has melted, remove it from the skillet. Let it sit for a minute, then cut it in half. Serve it hot with a side salad or your favorite fries.