Mix all the meatball ingredients together in a large bowl and mix well with your clean hands for a minute or two. You want the mixture to be well integrated, but you don't want to overwork it or the meatballs will be tough.
Form into meatballs and bake: With wet hands or an ice cream scoop, form meat into about 16 plum-size balls and space them out in a 13-by-9-inch baking dish, or, if you have one, a mini-muffin tin.
Bake at 400°F until lightly browned, about 15 minutes.
the sauce: While meatballs bake, heat the olive oil in a sauté pan over medium-high heat and sauté the onions until they just start to brown.
Add the garlic and cook for 1 minute.
Add the minced chipotles, the can of tomatoes, oregano or mint, and beef broth.
Mix well and add salt to taste. If you want more chipotle flavor, add the reserved chipotle sauce spoonful by spoonful, mixing and tasting between spoonfuls. Simmer the sauce uncovered as the meatballs cook.
Toss meatballs with sauce to serve: When meatballs are ready, put them into the sauce and toss to coat. If the sauce is too thin for your taste, continue to boil it down for a few minutes. Otherwise, serve with rice, tortillas or polenta.
