Boil a large pot of water on the stove.
Peel the onions, and place them into the boiling water for 12-14 minutes.
Remove, drain and slice the onions.
Heat the oven to 350 degrees.
Melt 1 Tbsp butter in a pot over medium heat.
Mix in the flour, and saute for 1-2 minutes.
Slowly whisk in the milk until well combined and thickened.
Season with salt and pepper to taste.
Add a layer of onions to the bottom of a small casserole dish or pie plate.
Top with a layer of peanuts and then some of the sauce.
Repeat the layers, with the sauce being on top.
Mix the remaining butter, and mix it with the breadcrumbs.
Sprinkle the crumb mixture over the casserole dish, and bake for 20 minutes.