If I'm using the giblets and neck, I place them in a medium saucepan with the chicken broth and bring it to a gentle simmer. I let this cook for about 10 minutes while the turkey rests, which pulls all that deep flavor into the broth. Once done, I pull out the neck, pick off any meat, and dice the giblets into small pieces to stir back in later.
While the broth simmers, I carefully pour the drippings from the roasting pan into a separator or a heatproof bowl. I let the fat rise to the top, then skim it off, keeping the flavorful liquid underneath. I pass everything through a fine mesh strainer so there are no burnt bits or stray herbs left behind.
In the same saucepan, I whisk the flour into a bit of the reserved turkey fat until it forms a smooth, thick paste. If the mixture looks greasy or too wet, I add a touch more flour until it comes together into a paste that coats the whisk.
I slowly pour the warm giblet broth and strained drippings into the roux, whisking constantly so no lumps form. I keep the heat at medium and keep whisking until everything is fully combined into one smooth mixture.
I let the gravy bubble gently for about 10 minutes, stirring often. If it looks too thick, I splash in a little more broth; if it's too thin, I just let it simmer a few extra minutes until it coats the back of a spoon.
Finally, I stir in the diced giblets if I'm using them, then taste and season with salt and pepper. Since the drippings are already salty, I always taste before adding more. I pour it into a warm gravy boat and serve it immediately alongside the turkey and mashed potatoes.