Preheat oven to 375°. Butter a 1½-quart baking dish.
In a large saucepan, bring onions and water to cover to a boil over medium-high heat. Cook until tender, about 5 minutes; drain.
In a large skillet, melt butter over medium heat. Add onion; cook for 5 minutes.
In a medium bowl, whisk together eggs and evaporated milk. Add onion, half of crushed crackers, cheese, salt, and pepper. Spoon mixture into prepared dish.
Bake for 35 minutes. In a small bowl, stir together melted butter and remaining crushed crackers. Sprinkle onto casserole, and bake until lightly browned, about 15 minutes more.
Recipe by Paula Deen Magazine at https://pauladeenmagazine.com/vidalia-onion-casserole/