No extra calories in this quick idea using ingredients already in your meal. When you've finished cooking potatoes with your roast beef, pork tenderloin, chicken or turkey, remove all of the vegetables from the drippings. Return some potatoes to the drippings & whizz them up with a hand blender. The consistency becomes just like gravy & doesn't add unnecessary flour/cornstarch etc calories. Just plain good food that you were already going to eat!
If you don't have a hand blender, a regular counter top blender will do just fine.