30 minutes before starting, take the green bean bags out of the freezer and let thaw.
melt 1/2 the butter and whisk in flour to create a rue.
whisk in salt, pepper, sugar, and onion.
add green beans and warm through.
remove from heat and stir in sour cream.
use 2 tablespoons of butter to grease casserole dish.
spread green bean mixture into dish, set aside.
crush cornflakes in a zip lock gallon bag.
melt remaining butter, and pour into bag of cornflakes.
layer shredded mozzarella on top of green beans.
layer crushed buttered corn flakes on top of mozzarella.
cook at 400 covered for 45 minutes, then uncovered for 15 until cornflakes are golden.