Chicken Gravy

So, we were having roasted chicken, again, this evening with some spaghetti squash, and broccoli, and I really felt like gravy. Gravy in general has been a problem for us given N's sensitivities to thickening agents...until now! This got rave reviews, even from our guest, who eats regular food!
I am going to list what I used, but I have a feeling you can change it up a bit!
The neck and gizzards of one chicken

1/4 onion chopped
2 stalks celery
1/2 carrot, peeled, chopped
1/2 bulb elephant garlic (probably 1 normal clove)
1/4 cup chopped fennel. (we are using this later in the week for a soup...)
1 Tbsp Butter
Salt and pepper to taste
Drippings from one 5-7lb chicken stuffed with celery stalks/leaves

In a 2 1/2 quart pan place the neck of the chicken, cut up, in the pot. Cover with several inches of water. Bring to a boil and skim any scum that rises to the top. Allow to simmer covered until water is an inch above the neck. (about 30-45 mins.) In the meantime pre-heat a cast iron skillet. Place 1 tbsp of Butter in the skillet and add the chopped up giblets, celery, garlic, onions, fennel and carrots. Saute until browned slightly and soft.
Remove the neck from the water and add to the skillet to remove juices from the bottom of the skillet. Transfer the sauteed mix back into the pot. Take out your immersion blender and blend the mixture with the water. It should produce a thicker looking stock. Make sure all is blended well. Once blended allow to simmer uncovered for about a 1/2 hour. It will reduce quite a bit and that is okay!

When the chicken is done, add the drippings from the pan into the gravy mix. Add Salt and pepper to taste. I blended the fat in for a more even consistency. Enjoy!