1. Melt butter in a saucepan, and scatter the flour over the top. Stir with a wooden spoon over gentle heat for 3-4 minutes, until lightly golden.
2. Add the hot stock slowly, stirring constantly. Whisk in Vegemite, tomato sauce and Worcestershire sauce and simmer gently, for 10 minutes, whisking occasionally until thickened.
3. Serve hot with roast meat.