I like to use the immersion blender for this soup because I hate spooning hot liquid into the blender and I also worry about the mixture exploding in my face from the pressure that builds in the blender (this happened to me when we were cooking in the professional kitchen). However, you can use a traditional blender (with caution). To be safe with a traditional blender, carefully spoon in the cooked cauliflower and hot liquid into the blender, being sure to not overfill the blender. Take the small plastic top out of the blender (or find another way to vent the top if possible). You will want to cover that hole at the top of the blender with a clean kitchen towel to avoid it exploding on the ceiling. If you cannot vent the blender, only transfer about 1/3 of the soup to the blender at a time and blend until smooth in batches.