Brown the beef: Heat the olive oil in a frying pan over medium-high heat. Add the beef in batches and brown it well on all sides this is where a lot of the flavour comes from, so don't rush it. Transfer to your slow cooker.
Cook the vegetables briefly: Add the onion and mushrooms to the same pan and cook for about 3–4 minutes, until the onion starts to soften. Add the garlic and cook for another 30 seconds, just until fragrant.
Add the tomato paste: Stir in the tomato paste and cook for about 1 minute. This takes away the raw tomato-paste flavour and gives the stew a richer, deeper taste.
Deglaze with the wine: Pour in the ½ cup dry red wine and scrape up all the browned bits from the bottom of the pan that's where the flavour is hiding. Let it bubble for 1–2 minutes.
Fill the slow cooker: Add the onion, mushroom and wine mixture to the beef, followed by the carrots, beef stock, thyme, bay leaf, pepper, salt, brown sugar and Worcestershire sauce. Stir everything together.
Slow cook for 8 hours: Cover and cook on LOW for 8 hours, until the beef is beautifully tender.
Thicken the stew: About 20–30 minutes before serving, mix 1 tablespoon cornflour with 2 tablespoons cold water until smooth. Stir the slurry into the stew, replace the lid, and continue cooking until the sauce thickens. Remove the bay leaf.
Serve with the green beans: Steam the green beans separately and serve alongside the stew, for a bit of fresh crunch against all that richness.