Encountering lumps or a grainy texture in your roux can be frustrating, but fear not—it's fixable. If you notice lumps forming as you whisk in the flour, pause and remove the saucepan from the heat. Gradually add the liquid (milk) while whisking vigorously to break down the lumps. If lumps persist, you can strain the mixture through a fine-mesh sieve to remove any clumps before continuing to cook.