While your turkey or chicken is baking, simmer the gizzards in water with an onion.
Once the turkey/chicken is done remove it from the roasting pan and place on top of the oven with both burners on low.
As the pan heats up, you'll be able to scrape the cooked on bits from the turkey/chicken.
Remove the gizzards and most of the onion from the simmered water and pour into the roasting pan.
Meanwhile, start the roux by melting ¼ cup of butter in a small saucepan.
Add in the 2 tablespoons of flour and stir to combine it with the butter.
Over medium heat add in the 1 cup of milk and continuously stir to create a rue that thickens and has some texture to it.
Before I pour the roux into the roasting pan, I salt the pan. We like things salty so I would say I add in about 2-4 teaspoons of salt, but this should be salted to your liking.
Combine the rue with the broth in the roasting pan and continue to stir until it is well combined.
I always use a gravy separator before pouring the gravy into my serving dish so that there are not any unwanted chunks and it separates the gravy from the fat.