Preheat oven to 400 degrees F and line two sheet pans with parchment paper.
Mix together the white cauliflower, garlic, and 1 tablespoon of oil and spread evenly onto one pan. Mix the purple cauliflower or broccoli with the remaining tablespoon of oil and spread onto the other pan. Roast 25-30 minutes, until the veggies are softened but not crisp.
Meanwhile, cook pasta in a large pot of salted boiling water according to package directions.
Blend the roasted white cauliflower mixture, milk, lemon, salt, pepper, and nutritional yeast together in a high-speed blender or food processor.
Mix your desired amount of sauce with the cooked pasta (we love creamy pasta, so I use all of it, but you may choose to save a bit). Stir in the purple cauliflower/broccoli, and top with fresh parsley and a drizzle of olive oil, if desired. Enjoy!