sentence: in a hot pot add butter flour whole milk and kosher salt sentence: simmer the mixture and add grated parmesan cheese and gruyere cheese and cook on low heat sentence: put butter on the grill and toast slices of sourdough bread and black forest ham sentence: add more gruyere cheese on the ham and apply dijon mustard on the bread sentence: put the ham on the bread and pour some bechamel sauce on the bread sentence: put the sandwich in the oven to toast the cheese