Melt 2 tablespoons butter in a skillet over medium heat. Whisk in the flour and cook for 2 minutes until tan.
Slowly whisk in the cooking liquid, Worcestershire and pepper. Simmer for 4 to 6 minutes until the gravy coats a spoon.
Pour the gravy into a slow cooker, add the cooked beef and turn gently to coat. Cover and warm on low for 20 to 25 minutes, just until the center of the meat reaches 165°F.
Spread the bread lightly with softened butter and toast it under the broiler or in a skillet until golden.
Put one toast slice on each plate, divide the hot beef over it and spoon on enough gravy to cover the meat without flooding the plate.