The only place for lumps to come from is the flour. It is important to get the roux smooth (fat first, then flour, lots of whisking) before adding broth to form velouté. If there is too much fat in the broth that will also lead to an odd texture but I wouldn’t call that “lumpy.” Be sure to fully cook the roux before adding broth. I’ve had some trouble with salt so be careful if you use bouillon. I use Kitchen Basics ‘No Salt Added’ with good results. Salt, if you need any at all, goes in at the end.
I use ‘whisk’ as a verb, not a noun. I usually use a fork in a stainless steel pot or cast iron pan. When my only option is non-stick I use a wood or silicone spatula. With care you can get a lot of muscle into the roux and ultimately the velouté without making a mess.
My wife has bursitis and carpal tunnel so we tried a bunch of mechanical aids before she gave up and I became saucier. grin I only have some early arthritis but no pain, no gain. Getting older is not for the faint of heart.
Hope this helps.
