Pour 2 cups strained broth from roast beef into a crock pot and set to high heat.
Now take another pan and melt butter in it over medium-low heat.
Once butter is melted, whisk in the flour and cook for 3-5 minutes until combined and starting to bubble. Don’t let the flour darken at this stage.
Now pour 1 cup of the hot roast juice into the flour mixture and mix well.
Pour the mixture into the crock pot with the remaining roast juice.
Whisk to combine until smooth.
After that, cover and cook over high heat for 30 minutes to 1 hour until thickened.
Now uncover and allow to cool slightly and season with pepper and salt to taste.
Serve warm with the desired meal.