Melt butter in large skillet over medium heat. Cook onion and garlic 10 min. until soft and tender. Stir in tomato paste. Cook 2 to 3 min. Stir in beef broth; bring to a boil. Reduce heat to medium; simmer until liquid is reduced by about one-third.
Whisk together flour and 3 tbsp (45 mL) water until smooth. Whisk flour slurry into broth mixture; bring back to a boil. Reduce heat to medium; simmer about 6 min. until thickened.
Meanwhile, skim fat from pan drippings, discarding fat. (Note: If pan drippings are stuck to roasting pan, add 1/4 cup (60 mL) hot water and scrape with wooden spoon to release.) Strain drippings and add to gravy. Bring back to a simmer; check that gravy registers 74˚C (165˚F) on an instant-read thermometer. Serve with roast.
If pan drippings are not available, this gravy is also delicious made without them.
During simmering, add a splash of red wine, beer, port, sherry or brandy for added flavour.