Here, for a while at McDonald’s there was an 🍔 called “the 1955” and it was the best, big pieces of onion, an special sauce, buns and big piece of beef with bacon (for Europe standards anyways) it disappeared once and came back for an encore only to be removed again and never return.
I’ve tried. The thing that’s hard to replicate is the beans, actually. Though I’ve mostly used canned refried beans; I’ve been meaning to get a can of whole pintos and mash them myself, and see if that helps.
You’ll probably want to start with dry beans. Canned ones are likely just going to be beans boiled in regular water. Meant to be an ingredient in something rather than the star. But if you make from scratch you can add in flavors: onion, garlic, etc.
Plenty of recipes online.
When making refried beans make sure to use pork fat of some kind. I use bacon fat.