In a sauce pot, heat milk over medium until warm. In separate small pot, melt butter over medium heat. Add the flour, reduce the heat to low and cook, whisking continuously, about 2 minutes. Whisk in warm milk until smooth.

Add your nutmeg & salt and simmer whisking continuously, until thickened. Remove from heat and add 1/4 cup of gruyere. Whisk mixture until smooth.

Set broiler on high. Lay bread out on a baking sheet, add 3 slices of ham to each slice of bread. Spoon sauce on top of ham. Divide remaining gruyere between the 4 sandwiches. Broil until cheese melts and is a golden brown, about 3-4 minutes.