Using a splash of the vegetable broth, sauté the onion, carrot, and garlic in a skillet over medium heat, until the onions are translucent and the carrots softened, about 8 minutes.

Sprinkle the flour over the cooked vegetables and stir to coat.

Add the remaining vegetable broth, mushrooms, poultry seasoning, salt, and pepper. Bring to a boil, then immediately turn down the heat, partially cover and cook for 10 minutes. Stir occasionally.

If you want, remove some of the mushrooms before blending. Add the mushrooms to a blender and blend until smooth. Transfer to a gravy boat and add the reserved mushrooms.