In a medium sauce pan add broth, garlic powder, onion powder, thyme (if using), salt, pepper and lemon juice. Heat to medium and bring to a boil.
In a small bowl whisk cornstarch with 2 tablespoon of water until smooth, to create a slurry to thicken the gravy.
Add slurry to broth, and whisk immediately to combine. Continue to boil and thicken up for 2-3 minutes.
Whisk in butter to combine, if using, and season to taste with salt and pepper. Serve immediately.
If you are making this for a roasted chicken or turkey dinner you should absolutely use the pan drippings! Measure out the pan drippings and add additional turkey or chicken broth to equal 2 cups of liquid.