A while back I was telling a friend how to make something and I said “you start with a nice rich brown roux” to which she responded “WTF is a roux”. Basically a roux is flour and some type of fat/grease combined. For me a 1 to 1 ratio typically works best. So 1 tablespoon of butter with one tablespoon of flour. To make a roux you melt the fat and than add the flour to it so that all the flour is soaked up into the fat. Fundamentally, you make a roux to act as a thickening agent for some other liquid you are going to add to the dish. If you make a roux right when you add the liquid and stir (sometimes for quite a while) the liquid will thicken and you won’t have lumps.
A roux is the basis for a lot of dishes. Pretty much anything that involves a white sauce, like Mac and cheese, needs a roux. A white sauce is roux plus milk. So all cream based soups involve a roux. Etouffe and creole also require a roux. For these dishes, you cook the flour longer to get a darker color to the flour. This adds a richer almost nutty flavor to the dish. Also for those of cooks who want to make gravy not from a packet? You’ll need a roux. In this case the meat drippings are the grease instead of butter.
Four tips from me on avoiding clumps. First, even heat at the right temperature. If your heat is too hot or not hot enough things will go sideways quick when you add the liquid to the roux. For me only a gas stove will do. I have a much tougher time with electric. When I have to use electric heat I always side towards a pan too hot because electric stoves don’t increase the heat quickly enough to compensate for heat too low. If the heat is too hot stir like crazy! Second tip. Make sure whatever liquid you are adding is at room temperature. Having liquid that is too cold combined with heat not hot enough equals lump-storm. Third tip. Use a whisk not a spoon to stir. This can help work little lumps out. If you have non stick pans get a silicon whisk. Final tip. Be patient and keep stirring. I can’t tell you how many times with gravy especially where I freaked out and thought it wasn’t going to thicken and screwed it up by trying to add more flour. THIS WILL EF EVERYTHING UP. Just take a breath and keep stirring 8/10 times it will be fine. Too thin is better than pasty lumps.
The more you make rouxs the more confident you will become and the less you’ll worry about lumps and if things are thickening.