Cut the beef into large chunks. Season with salt and pepper.
Peel and finely chop the onions.
In a large pot, brown the beef pieces on all sides in 0.7 oz of lard over high heat for 5 minutes. Remove the beef and set aside.
Remove excess fat from the pot without cleaning it.
In the same pot, sauté the onions in 0.7 oz of lard with a pinch of salt over medium-high heat for 5 minutes, stirring regularly with a wooden spoon.
Add the flour and brown sugar, and cook for 1 minute, stirring constantly.
Add the mustard and vinegar, then mix well.
Return the beef to the pot, along with the thyme and bay leaf. Pour in the water and beer. Cover the pot.
Bake at 302°F (150°C) for 3 hours.