Method

1. Preheat an oven to 400 degrees.
2. Toss the trimmed and halved Brussels sprouts in olive oil and liberally season with salt and pepper.  Transfer them to a 9×13 casserole dish and roast for 20-25 minutes until the edges start to brown and the sprouts are just tender. 
3. Next, make the cheese sauce. Start by cooking the bacon over medium heat in a large skillet. Cook until crispy and then remove from the skillet to drain on paper towels. 
4. Next, add the shallot and garlic to the skillet and cook until the shallot becomes translucent, around 3-4 minutes. 
5. Next, stir in the arrowroot starch until well combined and cook for 1 minute. 
6. Whisk in the coconut milk, chicken broth, dijon mustard, thyme, nutmeg, salt, pepper and let the sauce simmer until thickened, around 5-10 minutes. 
7. Lastly, stir in the shredded parmesan cheese and half of the crispy bacon. Pour the sauce evenly over the Brussels sprouts. Top with shredded gruyere cheese and remaining crispy bacon. 
8. Bake the casserole at 400 degrees until the cheese is melted and the sides are bubbly, around 10-15 minutes. Let the au gratin cool slightly before serving and enjoy!