Preheat oven to 425. Roughly chop cauliflower, celery, and onion. Oil cookie sheet/roasting pan. You can salt and pepper this too if you prefer.
Place vegetables on the pan and cook in the oven for 30 minutes or until tender and crisp on the end.
Make a roux: Heat your soup pot on medium heat with butter. Whisk in 3 tbsp flour until starting to ball up. Add one cup at a time to butter mix whisking well. Don't leave the pan, continue to whisk until you have a thick milky sauce.
To the roux, add salt and pepper and red pepper (sub cayenne for more heat).
When the vegetables are done, add to roux mix. Mix with an immersion blender. If you don't have an immersion blender, a food processor does well; just make sure you cool the soup before blending. Do not over mix. I prefer some roasted chunks and not completely smooth.
Mix in sliced gouda leaving some for garnish. Garnish with fresh parsley or bell pepper on top.