Heat the vegetable oil in a large skillet over medium-high heat and brown the ground beef in batches, breaking it into small crumbles with a wooden spoon, about 8 to 10 minutes, until no pink remains; drain off excess fat.

Add the diced onions and minced garlic to the skillet and cook for 4 to 5 minutes, stirring occasionally, until the onion turns soft and translucent.

Sprinkle in the chili powder, cumin, smoked paprika, oregano, cayenne, salt and black pepper; stir and toast the spices for 1 minute until they smell fragrant rather than raw.

Transfer the beef and onion mixture to a 6-quart slow cooker.

Pour in the crushed tomatoes, tomato sauce, beer (or broth) and kidney beans, then stir everything together until evenly combined.

Cover and cook on low for 6 to 7 hours, or on high for 3 to 4 hours, until the beef is fork-tender and the chili has thickened enough to coat the back of a spoon.

About 30 minutes before serving, whisk the masa harina with the water until smooth, stir it into the chili, and cook on high, uncovered, for 20 to 30 minutes more, until visibly thickened.

Taste and add more salt if needed, then switch the slow cooker to the warm setting and stir every 30 minutes while guests serve themselves.