Place the juices in a saucepan and heat on medium or medium-low heat. (Sometimes I’m impatient and I’ll turn it on medium-high heat so it’ll heat up faster).
In a separate container with a lid (a mason jar works great), shake together the all-purpose flour and about 1 to 2 cups of cool water (I usually use some the cooled juices just for that purpose so as to keep the flavor intact…once I forgot to let the juices cool down and burned my hand because the jar got so hot. Don’t do that.). This is what’s called a ‘slurry’ – adding the thickener (flour) this way helps prevent lumps from forming.
Once the drippings in the pan are lightly bubbling, slowly add the slurry mixture to the gravy pan, stirring constantly (I use a whisk to make sure no lumps start to form). If it starts to thicken immediately, stop adding the remaining slurry, you may not need to use the whole amount depending on how much or little drippings were in the pan.
Simmer gently about 10 minutes to cook the flour all the way through (undercooked flour gives off a raw taste). Salt and pepper to taste. If you find that your gravy isn’t thickening to your specifications, add more slurry until it does. If it gets too thick, you can water it down a bit to thin it out, or add more of the pan drippings.
Pour the gravy into a warmed gravy boat or wide-mouthed pitcher for serving. If lumps do develop, you should be able to use a wire whisk to remove them, or you can ‘cheat’ and pour the gravy through a fine sieve to eliminate any lumps before putting it in a gravy boat or whatever container you’re going to use to serve it. Not that I’ve ever had to do that…very often.
Remember that gravy will continue to thicken after it has been removed from the heat.
Instead of using regular flour, I found this awesome stuff by Gold Medal called ‘Wondra’ – it’s Quick-Mixing Sauce & Gravy Flour that dissolves quicker in liquid than flour does, and it doesn’t give you that ‘flour’ taste in your gravy or sauces. It looks like this:
Using the Wondra I’ve found you don’t have to simmer the gravy for a full 10 minutes to eliminate the flour taste, because it doesn’t have that heavy flour taste to begin with. Just simmer until thickened.