Making a roux is a simple yet essential technique for thickening sauces and gravies. Here's how to make a roux:

Ingredients:
- All-purpose flour
- Fat (butter, oil, or rendered animal fat)

Instructions:

1. **Heat the Fat**: In a saucepan or skillet, heat the fat over medium heat until it's melted and hot. Butter is the most commonly used fat for roux, but you can also use oil or rendered animal fat for different flavors.

2. **Add the Flour**: Once the fat is hot, sprinkle in an equal amount of all-purpose flour, stirring constantly with a whisk or wooden spoon to combine. The ratio of fat to flour is typically 1:1 by weight or volume.