Collect ingredients: pan drippings, butter (optional), all-purpose flour, salt, black pepper, broth/stock (beef/chicken/vegetable), optional aromatics (garlic/onion), optional herbs (thyme/rosemary), optional splash of wine or vinegar
Strain drippings through a fine-mesh sieve into a measuring cup; skim off excess fat
Measure fat and drippings total; aim for about 1/4 cup fat per 2 cups liquid (adjust as needed)
Make roux: melt butter (if needed to reach fat amount) in a saucepan over medium heat
Whisk in flour (typical ratio: 1/4 cup fat + 1/4 cup flour)
Cook roux, whisking constantly, until light golden and fragrant, 2–5 minutes
Reduce heat to low
Gradually whisk in warm broth/stock a little at a time to prevent lumps
Whisk until smooth; simmer until thickened, 3–8 minutes
Season with salt and black pepper to taste
Taste and adjust consistency with more broth (thinner) or simmer longer (thicker)
Stir in drippings at the end (or whisk them in early if your roux is already smooth)
Add optional flavor boosters: a splash of pan drippings, wine, or vinegar; a pinch of thyme/rosemary; roasted garlic/onion paste
Finish by whisking briefly and pouring immediately; keep warm until serving