Set oven to 400 degrees F.

Butter a 13 x 9-inch baking dish.

In a heavy-bottomed medium-size saucepan, melt the 1/4 cup butter, whisk in the thyme, nutmeg, fresh garlic, cayenne pepper and black pepper; whisk/mix for 2 minutes.

Add/whisk in the flour, mix for 2-3 minutes.

Slowly add/whisk in the half and half cream; whisk on med-low heat, until a light boil and thick; reduce heat to low, contine to whisk and cook for 3 minutes.

Remove from heat, add in the grated cheddar, Parmesan cheese, green onion and the Dijon mustard (if using); mix until all the cheese has melted; season with salt and more black pepper to taste.

Transfer the mixture to a large bowl.

Mix together the sauce, cooked pasta and the cooked, drained cauliflower; toss to combine.

Transfer and spread the mixture into a prepared greased baking dish.

In a small bowl, combine the bread crumbs, 1-2 Tbsp Parmesan cheese and the melted butter.

Sprinkle over the cauliflower mixture in the baking pan.

Bake for 20 22 minutes, or until hot and bubbly.