Place onion in a 13x9-inch casserole dish and drizzle with melted butter.
In a large bowl, mix together cream cheese, milk, bacon, pimientos, salt, and pepper. (The mixture should be thick like a paste.) Spread cream cheese mixture over onions and cover with foil.
Bake for 30 minutes. Remove from the oven and sprinkle with Cheddar. Pop the casserole back in the oven and bake until cheese is melted.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/brenda-gantts-onion-casserole/