Brown and mostly drain hamburger (do not completely drain or hambuger gets too dry). ( How much hamburger depends on the size casserole you want. 1lb serves 2 or 3, 2 lbs serves 4 - 6) You are the best judge of how big to make it! Spread browned hamburger in the bottom of casserole dish.
I use canned corn, drained. 1 can for each pound of hamburger. You may add more or less, depending on taste. Leftovers work fine! Put layer of corn over hamburger. It doesn't have to be thick, just spread out. Season with salt & pepper.
Mashed potatoes can be leftovers, instant, or freshly made. Make them the consistency of oatmeal, don't want them too firm, but not too runny! Spread layer of mashed potatoes over corn. Spread out like icing a cake. Not too thick, but make sure corn or hamburger isn't showing through.
May top with pats of butter.
Bake in 350 oven for 30 minutes or until bubbly. May lightly brown top.