Pretzel Crusted Chicken Nuggets with Easy Cheese Dipping Sauce

oil, for greasing pan

panko crumbs

salted pretzel crumbs*

coarse salt and fresh ground black pepper

+ ½ pounds boneless chicken breasts

eggs

all-purpose flour, plus more if needed

butter

all-purpose flour

milk

dijon mustard, optional

heaping cup fresh shredded sharp cheddar cheese