Season beef liberally with salt and pepper and gently dust with a bit of flour.
Over medium-high heat your pan and add the cooking oil and nicely brown the beef on both sides. Remove to a plate.
Lower the heat to medium. Saute the onions with the thyme (if needed add a little bit more cooking oil).
When the onions are translucent stir in the flour, cook for about 1 minute and deglaze with some of the stout, scraping off brown bits from the bottom.
Add the rest of the stout, the brown sugar and bay leaves, increase the heat and stir. Add back the beef and bring to a boil. Cover and bring to low.
Cook for about 3 hours or until the meat is very tender. You may start checking on it shortly after the 2 hour mark to get an idea of how much longer you want to cook it.
Discard the bay leaves and thyme sticks before serving