Heat 1 tablespoon butter (or oil) in a large saucepan over medium-high heat until melted. Add the onion and sauté for 5 minutes, stirring occasionally, until softened. Add garlic and sauté for 1-2 more minutes, stirring occasionally, until cooked and fragrant
Add in the pinto beans, veggie stock, chipotle chili powder, cumin and oregano, and stir to combine. Continue cooking until the mixture reaches a simmer.
Remove pan from heat. Use a potato masher or a wooden spoon to mash the beans to your desired consistency. (Or if you would like them to be super-smooth, you can purée them in a food processor until smooth.)
Stir in the remaining tablespoon of butter until it is melted and well-combined. Taste and season the beans with lime juice, salt and pepper, to taste.
Serve warm, topped with any garnishes you might like.