If you’re like, ‘what gravy??’, scoop out about a 1/2 cup of the broth and whisk in another tablespoon of cornstarch to get the lumps out. It’s a bit hard to do if you’ve got a bunch of veg in there but get at it. Add it back into the pot and stir. Wait a few minutes to thicken the mixture. Repeat as necessary until you reach desired thickness.