-
Preheat oven to 325F.
-
Mix flour with salt and pepper in a shallow dish. Toss beef cubes in flour.
-
Heat butter and olive oil in casserole dish over medium high heat. Add beef and brown outside but do not cook through. Remove beef from pan and set aside.
-
Add onions to pan and cook until slightly softened. Add the garlic and thyme, then add the beef stock, stout, beer, sugar and mustard, scraping up brown bits from bottom of casserole.
-
Return beef to casserole.
-
Let stew come to a simmer then place lid on top and place in oven for 2 hours, stirring once halfway through. Remove lid and cook for 30 minutes more to allow sauce to thicken. Watch closely though so that it doesn't dry out.