In a saucepan, melt the butter and sauté the garlic for 30 seconds. Add the flour, and cook while stirring for 1-2 minutes.
Add beef stock gradually while whisking. Then add the ketchup, Worcestershire sauce, salt, and pepper. Bring to a boil, cook while stirring until thickened (about 5 minutes). Taste and adjust seasonings to your preference.
Keep the gravy on the lowest heat possible to keep it warm until serving (if you're serving within 15 minutes).
Notes
Store the leftovers in the fridge in a sealed container for up to two days.This flour-based gravy freezes very well for months, you can freeze it in a container, freezer bags, or in ice cube trays.