Spread one side of each slice of sourdough with mayo.
Place one slice, mayo side down in frying pan over medium heat, spread 1 tbl POP MUSTARD on side facing up, stack with 2 slices cheddar, all the ham, last 2 slices of cheddar, spread remaining 1 tbl POP MUSTARD on sourdough and top with mayo side up.
Toast sandwich over medium heat until golden brown, approx. 2-3 minutes, flip to other side, pan can be covered at this point to help melt the cheese. Toast for 2-3 or until golden brown.