It's just a bechamel based cheese sauce with steamed broccoli added and then baked til bubbly...
she covers the top with slices of american cheese and then with panko crumbs mixed with melted butter for a topping...
I think the key is using mild cheddar (mild cheddar is a lot creamier than sharp or extra sharp) & real american cheese...
mixed 1/2 & 1/2...
My sisters recipe is a lot like many of my recipes...
we use the "that looks like about enough" measuring system for dishes we make a lot...
it is wonderful!

I think where I go wrong with her recipe...
I make the cheese sauce in a pot on the stove...
whereas she uses a double boiler to make the cheese sauce...
I just have no patience for a double boiler with that much volume...