Steam cauliflower until tender, about 8-10 minutes then remove from pan and set aside.
Whisk together milk and flour in a sauce pot over medium heat until mixture starts to thicken, about 5-7 minutes.
Add grated cheddar, garlic, dijon, nutmeg, salt and cayenne and whisk until cheese is melted. Stir in the steamed cauliflower and yogurt then puree until smooth with an immersion blender or pulse until smooth in a blender or food processor.
Add noodles and check for seasoning before pouring into a casserole baking dish.
In a small bowl, mix together panko, olive oil and parmesan cheese. Sprinkle mixture evenly over the noodles then bake for 15-20 minutes or until topping turns golden brown.