Once your turkey has cooked, remove it from its roasting pan and transfer it to a serving platter. While it rests, remove any large chunks (like veggies or meat) from its drippings. Then, using a rigid spatula, scrape off any browned (avoid any overly burned) bits off the bottom of the roasting pan. Pour these brown bits of flavor and the drippings into a large, 4-cup measuring cup.
Pour some poultry (chicken or turkey) stock into the measuring cup with the turkey drippings until the total amount reaches 4 cups. Set aside for a moment.
Melt the butter in a saucepan over medium-high heat. Whisk in the flour or oat fiber to create a roux and cook until just barely beginning to brown, causing a light, toasty, nutty aroma.
While whisking briskly and continuously, slowly pour the drippings and stock mixture into the saucepan with the roux. If any chunks of roux remain, try to smash as many as possible against the side of the pan with a spoon.
Bring the mixture to a boil, stirring constantly. Once boiling, continue to boil and stir constantly for about 2 minutes (give or take) or until the mixture begins to thickens slightly. You'll know it has thickened enough when you dip a metal spoon in and the gravy coats the spoon. The gravy will thicken more later as it cools.
Whisk in the cream, garlic powder, onion powder, cayenne pepper, parsley, salt, and pepper. Heat for an additional minute longer to just barely heat up the cream.
Remove from heat and transfer to a gravy boat or bowl.