How to make a proper brown gravy — it’s just like making a Béchamel cream sauce, except that instead of melted butter, you start with the fat and drippings collected in the pan after roasting meat:
Roast meat in a roasting pan, then remove from oven, let it rest for a bit, and remove it from the pan.
Put the roasting pan on the stovetop on medium-low heat.
Toss in flour, whisking it in, until the fat is incorporated (a few handfuls — depends how much fat is in the pan), and the flour is cooked (browned, no longer raw).
Pour in some milk (1/2 cup to a whole cup), whisk it in until smooth.
Scrape the roasted meat bits off the bottom of the pan as you whisk.
Add water (about a cup) in increments and continue whisking until texture is smooth and looks like gravy.
Your thickener could be corn starch. Your liquid could be stock. Use what you have.
If your roasted meat was salted and herbed or spiced, your gravy will already be seasoned and will not need any additional flavorings. If what you roasted was insufficiently salty or aromatic, now is the time to add whatever your gravy needs to amp it up. (Maternal unit liked Worcestershire sauce, with its delicious anchovy nature.)
Pour into gravy boat. Use ladle to skim any loose juices off the top of the gravy.