Prepare the beef. Trim excess surface fat and cut the beef into large, even chunks.
Layer the ingredients. Place the beef in a large, deep skillet or heavy-bottomed pot. Top evenly with sliced onions, then add pieces of butter and pour in the water.
Start simmering. Cover with a lid and simmer over low heat for 1 hour, allowing the beef to slowly tenderize and release its juices.
Add garlic and seasonings. Remove the lid and add the chopped garlic, salt, sugar, black pepper, and vinegar. Stir gently to combine.
Continue cooking. Cover again and simmer over low heat for another 1 hour, or until the beef is fork-tender and very soft.
Finish with parsley. Finely chop the fresh parsley and sprinkle it over the garlic butter beef just before serving.