- 8 slices gluten-free white sandwich bread, homemade or store-bought
- 2 tablespoons unsalted butter
- 3 tablespoons sweet rice flour
- 2 1/2 cups whole or 2% milk, warmed
- 1/4 teaspoon salt
- 1/2 teaspoon freshly ground black pepper
- 8 ounces Gruyère cheese, grated (about 2 cups)
- 1/4 cup freshly grated parmesan cheese
- Dijon mustard
- 1/2 pound thinly sliced ham
Preheat the oven to 425ºF. Place the bread on an 18 by 13-inch rimmed baking sheet. Bake, flipping once, until the slices begin to turn golden brown. Remove from the oven and set aside. Leave the oven on.
Prepare the sauce: In a small pot, melt the butter. Add the sweet rice flour. Cook for 3 minutes, whisking constantly. The paste will turn a light golden brown. In a slow and steady steam, add the milk. Cook, whisking constantly, until the sauce begins to bubble. Season with salt and pepper. Stir in 1/4 cup of the Gruyère and all of the parmesan. Whisk until smooth.
Make the sandwiches on the baking sheet. Spread a thin coat of mustard on each piece of bread. Place a few slices of ham and a generous sprinkle of Gruyère on each of 4 bread slices. (Reserve about one-quarter of the cheese.) Top with a second slice of bread, mustard side down. Spoon a generous amount of white sauce onto each sandwich. Divide the remaining Gruyère over the top.
Return the sandwiches to the oven. Bake for 5 minutes to heat.
Turn on the broiler. Broil until the cheese is melted, light brown, and bubbling. Serve immediately.