Preheat oven to 375 degrees F. Spray an 8x10- inch baking dish with nonstick cooking spray; set aside.

Add cauliflower to a pot of boiling water and boil for 5 minutes or until barely tender; drain and set aside.

In a saucepan over medium-high heat, melt butter. Whisk in flour and cook for one minute. Whisk in milk until smooth and cook for a few minutes until sauce has thickened. Add Swiss cheese, salt, pepper and nutmeg and stir until cheese is completely melted.

Toss cauliflower in cheese sauce then spread in prepared baking dish. Top with panko bread crumbs and spray generously with cooking spray.

Bake for 30 minutes then turn oven to high broil and broil for 1-2 minutes, until breadcrumbs are golden brown on top.