I call shenanigans! The soup is delicious, but that step at the end where you add butter/flour is completely incorrect. This is the basis for any béchamel sauce or gravy, but a cup of flour will NOT be incorporated into 1/4c of any fat. The ratio is normally 1 T fat (butter) to 1 T flour to 1 cup liquid. When mixed this way the "paste" will not take on any more flour than about a half a cup and even then it starts separating and turning into crumbles and will not blend into the soup without creating lumps. I tried this as written, even though I knew it wouldn't work and I am right. Even with a half a cup of flour, I had to add 2 cups of water, take it off the stove, use a stick blender to smooth the lumps, and then added maybe 1/4 of that into the soup. If you want to add this step, and it does add a lusciousness that elevates it from the standard lentil soup, I suggest 2 T butter and 2 T flour. If you toast the flour in the pan over medium heat while stirring before adding the butter, you'll cut down on time and have a better product.
But again, the soup itself is really tasty and has the perfect amount of spice. I used both french and brown lentils and added a half cup of chives and extra parsley since I'll soon lose my fresh herbs to frost.