Season the beef. Place the beef in a bowl and season it with salt, pepper, and extra virgin olive oil.
Brown the beef. In a large pot, over medium to medium-high heat, brown the beef. Work in batches. It should take about 3-4 minutes per batch. Do not attempt to brown all of the beef at once, which will steam-cook the beef rather than brown it. You want a crust on each piece of beef, as well as a fond on the bottom of the pot. Once the beef is browned, set it aside.
Deglaze with beer. Once the beef is browned, pour a splash of beer into the pot. Stir with a wooden spoon to deglaze the fond, or stuck-on bits of meat, that has developed in the pan. Do NOT discard this fond. It both flavors and colors the stew.
Sauté the onions. Reduce the heat to medium-low and add the butter to the pot with the fond. Once melted, add the onions and garlic and sauté until the onions begin to develop a soft, jam-like consistency (about 20 minutes). Equally, you can sauté the onions for longer to caramelize them further. Ensure the heat is low in order to not burn the garlic. If the pot becomes too dry, add a little extra virgin olive oil or butter as necessary.
Add the flour. Add the flour to the pot and stir to combine. The onion, garlic, and fond mixture should become dry at this point.
Add the liquid. Add the remaining beer and balsamic vinegar to the pot and stir to combine.
Return the beef. Return the browned beef to the pot.
Add the herbs, spices, and sugar. Add the herbs, spices, and sugar to the pot and stir to combine. Bring the pot to a boil and then reduce the heat to low.
Cover with a slice of brown bread. Spread a dollop of mustard over a slice or two of brown bread and place over the top of the stew.
Simmer for 2-3 hours. Cover the stew and simmer for 2-3 hours, or until the meat is fork tender, stirring occasionally. Remove the lid and simmer for another 30 minutes uncovered to slightly thicken the sauce.