Ingredients

2 tablespoons unsalted butter 

2 tablespoons all-purpose flour 

1 1/4 cups whole milk, warmed 

Coarse salt and freshly ground pepper 

12 small fingerling potatoes (or 4 to 5 ounces other small waxy potatoes), cooked until tender, smashed 

2 tablespoons extra-virgin olive oil 

4 slices (3/4 inch thick) day-old Tartine Bakery's Country Bread 

4 thick slices smoked ham 

8 slices Gruyere cheese (4 ounces) 

Preparation

Make the bechamel:Melt butter in a heavy saucepan over medium heat. Add flour, and whisk until mixture bubbles slightly, but has not started to brown, about 2 minutes. Whisk in milk. Bring to a boil to thicken. Season with salt and pepper. Remove from heat.

Make the croque-montagnarde:Preheat oven to 425 degrees. Toss potatoes with oil. Spread 1/4 cup bechamel onto each slice of bread, and top with 1 slice of ham, some potatoes, and 2 slices of cheese. Bake on a baking sheet until cheese is golden and bubbling, 12 to 14 minutes (start checking often after 8 minutes, and rotate sheet as needed for even browning).

Melt butter in a heavy saucepan over medium heat. Add flour, and whisk until mixture bubbles slightly, but has not started to brown, about 2 minutes. Whisk in milk. Bring to a boil to thicken. Season with salt and pepper. Remove from heat. Preheat oven to 425 degrees. Toss potatoes with oil. Spread 1/4 cup bechamel onto each slice of bread, and top with 1 slice of ham, some potatoes, and 2 slices of cheese. Bake on a baking sheet until cheese is golden and bubbling, 12 to 14 minutes (start checking often after 8 minutes, and rotate sheet as needed for even browning).