Season the beef with the salt and pepper. In a large skillet (or your slow cooker if it has a saute option), sear the beef on all sides, then transfer to the slow cooker.
Add the onion, carrots, potatoes, thyme, beef broth, beer, and tomato paste and stir to mix.
Cook on high for 6-8 hours.
Scoop out 1/2 cup of broth and whisk together with cornstarch to make a slurry, then stir the mixture back into the stew. Let cook briefly to thicken, then serve.